Showing papers in "Behavioral Ecology and Sociobiology in 1990"
TL;DR: The security model demonstrates that both detection and dilution are important in determining the frequency of vigilance behaviour but that the relative importance of these two effects changes across group size, with detection providing relatively less benefit as group size increases.
Abstract: Grouped individuals are less vigilant for predators than solitary conspecifics because (1) grouping increases the likelihood of predator detection (detection effect) and (2) grouping makes it less likely that any given individual will be preyed upon (dilution effect). However, many models of vigilance behaviour consider only the detection effect, and the interaction of the two effects has been insufficiently considered. I present two models of vigilance behaviour and test them using data on the vigilance of elk, Cervus elaphus. The first model, based on the detection effect alone, is implicit in many published formulations of the relationship between vigilance and group size. Although it predicts the direction of the relationship between vigilance and group size, it provides a poor explanation of the form of the relationship. The second model incorporates both detection and dilution effects. Regression analysis on this “security model” indicates that the model provides a good prediction of both the direction and the form of the relationship between vigilance and group size, explaining 69% of the variance in vigilance frequency. The security model demonstrates that both detection and dilution are important in determining the frequency of vigilance behaviour but that the relative importance of these two effects changes across group size, with detection providing relatively less benefit as group size increases. However, even when groups are large, individuals should exhibit at least some vigilance because although dilution alone provides much protection from predation, even a low level of vigilance greatly increases the likelihood that an individual will survive repeated predation attempts.
374 citations
TL;DR: Parentage of nestlings in a North Carolina population of indigo buntings was analyzed using DNA fingerprinting, finding that young males tended to be excluded less often than older males, wing length and weight were not associated with the frequency of exclusion, and weight and wing length of females also were notassociated with involvement in EPCs.
Abstract: Parentage of nestlings in a North Carolina population of indigo buntings (Passerina cyanea) was analyzed using DNA fingerprinting. Three minisatellite DNA probes (wild type M13, Jeffreys' 33.15 and 33.6) were used to analyze nuclear DNA isolated from muscle biopsies of 63 nestlings, their parents, and other local adults. Each probe detected approximately 15 scorable fragments per individual, with 18%–39% overlap between probes. The proportion of bands shared (using all fragments over all three probes) between presumably unrelated adults averaged 0.23. Of the 63 offspring analyzed, 35 had at least one fragment not present in either putative parent. The distribution of offspring with novel fragments was distinctly bimodal. The lower mode (offspring with 0, 1, or 2 novel fragments, N=41) fit a Poisson distribution, a pattern expected if mutation (estimated rate per fragment= 0.01) were the source of the novel fragments. The remaining 22 offspring had more novel fragments than could be explained by mutation alone (minimum of four independent fragments across all three probes,
$$\bar X$$
=8.2). A low band-sharing proportion with the resident male (
$$\bar X$$
=0.24) and high band-sharing with the resident female (
$$\bar X$$
=0.60) implicated extra-pair fertilizations as the source of all 22. Thus in this sample, 35% of all nestlings came from extra-pair fertilizations and none from intra-specific brood parasitism. Of 25 broods sampled, 12 (48%) had at least one excluded offspring. In 3 broods all of the offspring excluded the resident male. Band-sharing proportions between excluded nestlings within a brood could not distinguish between single and multiple extra-pair paternity. Although young males tended to be excluded less often than older males, wing length and weight were not associated with the frequency of exclusion. Weight and wing length of females also were not associated with involvement in EPCs. Six of the 22 excluded offspring (in 3 broods) shared a large proportion of bands and had fewer than four novel fragments when compared to the fingerprints of a neighboring territorial male, implicating those males as actual fathers. The parentage of the remaining 16 offspring (in 9 broods) could not be clearly assigned because (1) one or more neighbors were not sampled or (2) difficulties in scoring across gels prevented confident alignment of fingerprint bands, and insufficient DNA was obtained from muscle samples to allow reanalysis of potential actual fathers on the same gel as excluded nestlings.
363 citations
TL;DR: Behavioural observations show that EPP occurs through extra-pair copulation rather than rapid mate switching in a wild population of zebra finches, and is discussed in the light of what is known about the fertile period and sperm precedence patterns in this species.
Abstract: The frequency of extra-pair parentage in a wild population of zebra finches Taeniopygia guttata was examined by DNA fingerprinting. A total of 25 families, comprising 16 pairs of parents and 92 offspring (in broods of 1 to 6) were examined. Ten cases of extra-pair parentage, presumed to constitute intraspecific brood parasitism, were detected (10.9% of offspring or 36% of broods), including one possible instance of ‘quasi-parasitism’ (parasitism by a female fertilized by the male nest owner). The average number of parasitic eggs per clutch detected by fingerprinting was 1.10±0.32 SD, very similar to the one egg difference in average clutch size between parasitised (6.0±0.82) and unparasitised nests (5.0±0.95). Two cases of extra-pair paternity (EPP) were detected among 82 offspring whose maternity was confirmed: 2.4% of offspring, or 8% of broods. In both cases EPP accounted for only a single offspring within a brood. Behavioural observations show that EPP occurs through extra-pair copulation rather than rapid mate switching. The results are discussed in the light of what is known about the fertile period and sperm precedence patterns in this species.
269 citations
TL;DR: Analysis of whistle exchanges from 12 mothercalf pairs shows that signature whistles can remain stable for periods up to at least 12 years, and hypothesize that sex differences in whistle vocalizations may reflect differences in the roles males and females play in the social structure of the community.
Abstract: Mother-calf whistle exchanges were recorded from temporarily captured free-ranging bottlenose dolphins from 1975 to 1989. This is part of a long-term research project studying social structure and behavior of a community of approximately 100 dolphins in waters near Sarasota, Florida. Analysis of whistle exchanges from 12 mothercalf pairs shows that signature whistles can remain stable for periods up to at least 12 years. We looked for effects of vocal learning on the development of the signature whistle by comparing whistles of calves to those of their mothers. Eight female calves produced whistles distinct from those of their mothers, while four male calves produced whistles similar to those of their mothers. Male calves appeared to produce a greater proportion of whistles other than the signature whistle (termed “variants”). We hypothesize that these sex differences in whistle vocalizations may reflect differences in the roles males and females play in the social structure of the community.
251 citations
TL;DR: The promiscuous mating system demonstrated here would reduce the level of inbreeding in the population but still allow individuals the security of group-living in a stable year-round territory.
Abstract: Paternity likelihood was tested in a population of splendid fairy-wrens Malurus splendens by allozyme electrophoresis. A total of 91 offspring of 24 dams and 37 putative sires were typed at 10 polymorphic loci. All young were compatible with their dams but at least 65% were not fathered by any of the males in their group. A long-term study of this wren population has shown that the males are sedentary, show little evidence of dispersal and help care for the nestlings and fledglings in their group. Had the senior male sired all the offspring in his group, there would have been a high incidence of close inbreeding. The promiscuous mating system demonstrated here would reduce the level of inbreeding in the population but still allow individuals the security of group-living in a stable year-round territory.
246 citations
TL;DR: A dominant male that forms a coalition with a relative can expect to have longer reproductive tenure than in a troop with a non-relative, thereby producing more offspring and directly enhancing his fitness.
Abstract: Variance in male reproductive success in single and multi-male red howler (Alouatta seniculus) troops was examined through paternity exclusion using genetic markers. Coalitions of relatives were compared to coalitions of non-relatives with regard to duration, stability, and number of offspring expected for each participant based on paternity exclusion results. No evidence of paternity by males living outside of the troop was found. In multi-male troops, only the dominant male was found to father offspring conceived during his tenure. This was the only male observed to mount females. In both troops examined genetically wherein a status change had occurred, paternity changed with status. Coalitions of relatives and potential relatives lasted significantly longer than coalitions of non-relatives, and experienced fewer status changes between males. A direct advantage of forming a coalition for both dominant and subordinate red howler males resulted from the superior competitive ability of coalitions over single males in establishing and maintaining tenure in the limited number of female troops in the population. Although the mating success of a subordinate male in a coalition appears to be extremely low, his chances of achieving membership in a bisexual troop as a single male may be even lower. Since the majority of troops in the population during any given year were multi-male or age-graded male (85%–96%), the number of troops that a single male would be able to invade unaided was very small. A subordinate male may be able to assume dominance, particularly if he is a subadult. In coalitions in which males are related, the subordinate male will further benefit from inclusive fitness. A dominant male that forms a coalition with a relative can expect to have longer reproductive tenure than in a troop with a non-relative, thereby producing more offspring and directly enhancing his fitness. Anecdotal evidence suggests that males choose relatives over non-relatives as coalition partners when possible.
232 citations
TL;DR: Prospective models are developed for analysing sperm competition data so as to predict the underlying mechanisms determining paternity in multiply mated females and can be increased by manipulating the number of sperm transferred by each male.
Abstract: Prospective models are developed for analysing sperm competition data so as to predict the underlying mechanisms determining paternity in multiply mated females. The models require: 1) estimations of proportion of offspring sired by the last male to mate (P
2), 2) knowledge of the number of sperm transferred by each male, and 3) knowledge of the sperm storage capacity of the female, should this be limited. They will distinguish between “raffles” (sperm mixing without displacement) and sperm displacement mechanisms. The sensitivity of the techniques can be increased by manipulating the number of sperm transferred by each male. Typically, this can be done by manipulating copula duration or number of ejaculations, given a knowledge of the rate of sperm transfer. Data from two contrasting insect species are fitted to the models to demonstrate the techniques. These models are prospective only, and their limitations are discussed. The principal limitation is that we assume that sperm used for fertilization mix randomly in a “fertilization set” immediately prior to fertilization; in reality this may be difficult to identify. When sperm mixing is very rapid, the fertilization set will often be equivalent to the sperm stores, but with slow mixing, the fertilization set may be equivalent to a much more restricted zone and may change with time.
198 citations
TL;DR: Among the Kipsigis people of Kenya, women preferentially choose men offering high quality breeding opportunities, with respect to the number of acres available on which to settle as mentioned in this paper.
Abstract: In contrast to studies of birds, in mammals there is no clear evidence that polygyny evolved through female choice for males with high quality resources. Among the Kipsigis people of Kenya, polygyny may be a consequence of women's preferences for wealthy men, because strong correlations exist between land ownership and the number of a man's wives (Borgerhoff Mulder 1987 a), and the resources men hold are primary determinants of women's reproductive success (Borgerhoff Mulder 1987b). This paper has two aims: first, to test whether Kipsigis women prefer wealthy men by examining the sequence of marriages among a group of pioneers (Table 1) who established a settlement in the territory of their enemies (1930–1949); second, to determine whether women suffer reproductively as a result of polygynous marriage. Data show that Kipsigis women, or their parents on their behalf, preferentially chose men offering high quality breeding opportunities, with respect to the number of acres available on which to settle (Fig. 2) ; controlling for quality of breeding opportunity there is a preference for bachelors over monogamists over polygynists. Analyses of the full demographic sample show that there are reproductive costs associated with having a large number of cowives (Table 2), costs which women attempt to minimize through judicous marital choices. These results are discussed in relation to resource defence polgyny, female choice and, specifically, the polygyny threshold model.
195 citations
TL;DR: The results suggest that ecological factors set an upper limit to the number of spider monkeys that can associate and still efficiently exploit the available resources.
Abstract: In this paper I consider how the costs and benefits of group living in spider monkeys (Ateles geoffroyi) vary between troop members. The results suggest that ecological factors set an upper limit to the number of spider monkeys that can associate and still efficiently exploit the available resources. In addition, the needs of the individual appears to influence the type and size of the subgroup it chooses. Adult males band together, travel over a large area, and are frequently sighted near the community's boundary. In contrast, adult females spend more time solitary than males and have association patterns that are strongly influenced by the presence of a dependent infant. Females with dependent infants tend to travel in small subgroups or alone, avoid the boundaries of the community's home range, and exhibit a restricted pattern of use of their range. The results suggest that males may be attempting to locate females with which they can breed, while mothers attempt to protect their infants by avoiding conspecifics and potentially dangerous situations near territorial boundaries.
192 citations
TL;DR: It is shown that group living in alpine marmots has benefits during winter and indicates the additional importance of kin selection in marmot social evolution.
Abstract: Social groups of alpine marmots (Marmota marmota) were studied for 7 years. The groups consisted of a territorial pair and up to 18 lower ranking animals of various ages, mostly the pair's offspring (Tables 1, 2). Group members lived in a common home range and always hibernated together in one hibernaculum. Groups with older, subordinate animals experienced slightly higher summer mortality but significantly reduced winter mortality (Fig. 1). Infant winter mortality was further decreased if most older subordinates were potentially their full sibs (Fig. 2). Subordinate group members lost less mass during winter with increasing size of the hibernating group, but this trend was reversed when infants were present. Furthermore, augmented mass loss due to low hibernaculum quality became evident (Fig. 3). Apart from these effects, the presence of infants caused additional mass loss in potential full sibs. The opposite was found in subordinates certainly descending from other parents than those of the infants (Table 3). Winter mortality and mass loss data revealed (i) a general benefit of joint hibernation, (ii) an unavoidable cost of infants' presence to other group members, (iii) that only potential full sibs helped in warming infants, (iv) that helping was energetically expensive and increased infant survival. The evolution of postponed dispersal in ground-dwelling squirrels has been attributed to the direct fitness gained by enhanced reproductive chances of offspring when not expelled from the natal territory (Armitage 1981, 1987, 1988). This study shows that group living in alpine marmots has benefits during winter and indicates the additional importance of kin selection in marmot social evolution.
180 citations
TL;DR: Observations suggest that gravid females become less active or conspicuous on the surface to allow some species the advantages inherent in both high relative clutch mass when gravid and the increased energetic profitability of active foraging when not gravid.
Abstract: Female Eumeces laticeps experience a substantial decrease in running speed (ca. 25%) and an even greater loss of endurance (slightly over 50%) while gravid. Because some widely foraging lizards, including E. laticeps, rely primarily on running to escape predators, the decreases in speed and stamina may contribute to an increased risk of predation. However, observations suggest that gravid females become less active or conspicuous on the surface. Ambush foraging lizards rely relatively more on crypsis associated with immobility to avoid predation and thus can have greater average relative clutch mass (RCM) than active foragers. Behavioral compensation for locomotor impairment by becoming less active or conspicuous may allow some species the advantages inherent in both high relative clutch mass when gravid and the increased energetic profitability of active foraging when not gravid. As females gain weight during the breeding season, they may forage actively until the risk due to increasing locomotor impairment becomes too great and then change defensive strategy to greater reliance on crypsis. Without such a shift, widely foraging squamate reptiles may be less able than ambush foragers to exploit life-historical strategies demanding high current investment in reproduction.
TL;DR: Prolonged toleration of offspring in marmots was hypothesized to be a means of preventing dispersal of undersized young, or more generally (2) continued parental investment, increasing the probability of descendant survival and reproduction, but these hypotheses are not supported.
Abstract: Prolonged toleration of offspring in marmots was hypothesized to be (1) a means of preventing dispersal of undersized young (Barash 1974 a) or more generally (2) continued parental investment, increasing the probability of descendant survival and reproduction (Armitage 1981, 1987). These hypotheses are tested in this paper for one of the most social of marmot species, the alpine marmot. The animals studied lived in groups within territories defended by a dominant male and female, or as floaters lacking a well-defined home range. Offspring did not disperse before sexual maturity at age 2 (Fig. 1). Only territorial females bred, whereas territorial males were not able to monopolize reproduction likewise (Table 2). Dispersers had similar spring mass to nondispersers (Table 4). Hence, hypothesis 1 is not supported, at least not for adult-sized, > 2 years old animals. During their residency, 19% of subordinates obtained their natal territory or a neighboring one (Fig. 2). Long distance dispersal bore a high mortality risk. Thus, toleration of mature offspring could well represent parental investment. Other results, however, suggest additional influences on the timing of dispersal. (i) Males dispersed later than females (Fig. 3), possibly because of mate sharing by territorial males (see Emlen 1982). (ii) The higher mass loss of dispersers during the previous winter indicates that weak animals were forced to leave (Table 5) despite presumably lower chances of becoming territorial (Table 3). (iii) Subordinate animals which could not be the offspring of both territorials present were not more likely to disperse (Fig. 3). (iv) Lower dispersal rates when immatures lived in the group (Fig. 3) may indicate benefits from the subordinates' presence for rearing young.
TL;DR: It is shown how in one marriage cohort (1720–1750), family land ownership correlates with systematic fitness differentials, which means farmers have a greater long-term fitness, on the average, than members of non-peasant population, and farmers possessing better than average wealth achieve a greaterLong-term Fitness than farmers with medium-sized or small landholdings.
Abstract: On the basis of a family reconstitution study (Krummhorn, Germany, 18th und 19th centuries) it is shown how in one marriage cohort (1720–1750), family land ownership correlates with systematic fitness differentials. Farmers have a greater long-term fitness, on the average, than members of non-peasant population, and farmers possessing better than average wealth achieve a greater long-term fitness than farmers with medium-sized or small landholdings. The proximate causes herefore are to be found in both the varying patterns of marital fertility and in the differences in the marital and migration habits of the children from the various social groups. That is why the number of live births or even the number of surviving children is not the best estimate of a person's genetic contribution to the next generation of the local population. This can be shown by using a new algorithm for the assessment of long-term fitness differentials.
TL;DR: Putative fathers spent comparable amounts of time to females in the nest — presumably caring for the young — which supports previous laboratory reports of paternal care in this species.
Abstract: Home ranges, social organization, and nest co-occupancy of Peromyscus californicus were studied using radiotelemetry at the Hastings Natural History Reservation, California. Mated pairs were ascertained by the transfer of fluorescent pigments from lactating females to putative fathers. Mated pairs had largely overlapping home ranges that were not statistically distinguishable, whereas adjacent adults had mostly exclusive, statistically distinguishable home ranges. There was no difference in the mean home range of males and females, but mated females tended to have smaller ranges than their mate. Home range size was extremely variable (range: 150–3788 m2) and averaged 1161 m2 across all individuals. Male home range size was inversely correlated with population density, suggestive of a social influence on home range. Putative fathers spent comparable amounts of time to females in the nest — presumably caring for the young — which supports previous laboratory reports of paternal care in this species. All data collected in this study are consistent with previous suggestions that P. californicus live in semi-permanent family groups and are monogamous.
TL;DR: A model for honey bee colony defense involving at least two distinct groups of workers is developed and it is proposed that the non-guard defenders be called “soldiers”, due to their important role in colony defense.
Abstract: Summary. Some worker honey bees respond to major disturbances of the colony by flying around the assailant and possibly stinging; they are a subset of the bees involved in colony defense. These defenders have an openended age distribution similar to that of foragers, but defensive behavior is initiated at a younger age than foraging is. Behavioral and genetic evidence shows that defenders and foragers are distinct groups of older workers. Behaviorally, defenders have less worn wings than foragers, suggesting less flight activity. Genetically, defenders differ in allozyme frequencies, demonstrating different subfamily composition from foragers in the same colony. They also differ in allozyme frequencies from guards in the same colony, providing further evidence for division of labor associated with colony defense. We use this information to develop a model for honey bee colony defense involving at least two distinct groups of workers and we propose that the non-guard defenders be called "soldiers", due to their important role in colony defense.
TL;DR: Since male and female reproductive success is limited in Nicrophorus by access to suitable carcasses, many of the typical asymmetries in the costs and benefits of parental care are lacking, however since sperm displacement is not complete, paternity of the replacement clutch may be a factor encouraging male desertion before female desertion.
Abstract: Parental behavior that has an impact on the increased survival of offspring, an important factor in the evolution of parental care, can include both guarding and provisioning. The effects of these two components of parental care can be separated and quantified in the burying beetle Nicrophorus orbicollis in which both male and female cooperate to rear young. Although in the absence of competition, reproductive success is reduced by the presence of the second parent in the brood chamber, two parents dramatically reduce the probability that conspecifics will usurp the resource, replace either the male or female, kill the newly hatched brood, and produce a replacement clutch. After the establishment of the burial chamber (but not before) beetles appear to assist their mates in driving off intrasexual competitors. Male assistance in burial does not account for very much of the variance in the speed in which the carcass can be concealed nor are two parents essential to guard against insect predators. There were no significant differences in the duration of parental care by males paired with virgin and non-virgin females suggesting that paternity of the brood for which the male provides care is not a factor determining the length of care. Since male and female reproductive success is limited in Nicrophorus by access to suitable carcasses, many of the typical asymmetries in the costs and benefits of parental care are lacking. However since sperm displacement is not complete, paternity of the replacement clutch, for which the male does not provide care, may be a factor encouraging male desertion before female desertion. Other factors important in the evolution of paternal care, especially the probability of additional reproductive opportunities, are discussed.
TL;DR: Results of some experiments are reported that show that the positive effects of nutrient donation on female reproduction for one species of spermatophylax producing tettigoniid can be realized within 24 to 48 h.
Abstract: A recent debate has centred on the importance of paternal investment for the origin and maintenance of nuptial feeding in insects. Some authors have argued that the rates of nutrient incorporation are likely to be too slow to allow a male to fertilize the eggs that he helps to produce and cannot be considered as paternal investment. Here I report the results of some experiments that show that the positive effects of nutrient donation on female reproduction for one species of spermatophylax producing tettigoniid can be realized within 24 to 48 h. Furthermore, mating was found to induce a refractory period in the female that was longer than the time taken for the incorporation of nutrients and oviposition. Thus, the nurturant male is likely to fertilize the eggs even if last-male sperm precedence is high. The cost of spermatophylax production was manifest as a 5-day recovery period between matings. Thus males and their donations are likely to be limited resources for females resulting in a reversal of the typical sex roles.
TL;DR: The stability of the phenotypic distribution across generations, despite changes in P allele frequencies, was maintained by the production of small XX sons by Y-I and Y-L males, and there was no change in the distribution of male body size classes.
Abstract: In a natural population, we document changes in the frequencies of alleles influencing body size and size-correlated alternative male reproductive tactics, and we examine the possible role of sexual selection in producing these changes. Male swordtails (Xiphophorus nigrensis, Rio Choy) exhibit three body size classes (small, intermediate, and large) that primarily derive from allelic variation (s, I, L) at the Y-linked pituitary (P) locus. Some XX individuals are male. They are small and can be fathered either by XX or XY males. We compared the frequencies of Y-linked P alleles across two generations in a natural population. There was a significant decrease in the Y-s genotype relative to Y-I and Y-L genotypes. Laboratory experiments suggest that the disadvantage of Y-s resulted, at least in part, from female preference for larger courting males relative to small chasing males. All larger courting males are of the Y-I or Y-L genotypes. Although the frequency of Y-linked P alleles changed across generations, there was no change in the distribution of male body size classes. The stability of the phenotypic distribution across generations, despite changes in P allele frequencies, was maintained by the production of small XX sons by Y-I and Y-L males.
TL;DR: Spiders in the core of the colony have greater reproductive success, producing more egg sacs with greater hatching frequency, and show a spatial organization predicted by the selfish herd theory.
Abstract: Colonial web-building spiders respond to trade-offs between selective forces relative to spatial position within colonies and thus provide support for the selfish herd theory The size distribution of spiders within colonies of Metepeira incrassata, a colonial orb-weaver (Araneae: Araneidae) from tropical Mexico is nonrandom; larger (mature) spiders and females guarding eggsacs are more prevalent in the center, whereas more small (immature) spiders are found on the periphery Experimental field studies with spiders of selected size classes show that larger spiders actively and aggressively seek protected positions in the center of the colony webbing, even though prey availability and capture rates are significantly higher on the periphery Attacks by predatory wasps, other spiders, and hummingbirds are more frequent on the periphery than in the core of the colony Reproductive females on the periphery are at greater risk because they are captured more often than smaller spiders, and if their egg sacs consequently remain unguarded, chances of cocoon parasitism are increased As a result, spiders in the core of the colony have greater reproductive success, producing more egg sacs with greater hatching frequency Colonial spiders thus appear to be making a trade-off between foraging and protection from predation and show a spatial organization predicted by the selfish herd theory The influence of such trade-offs on individual fitness and the structure of colonies is discussed
TL;DR: Female burying beetles Necrophorus vespilloides Herbst (Coleoptera: Silphidae) were allowed to lay eggs on a carcass and their subsequent behavior towards larvae added to the carcass was observed, and most females killed and ate larvae that could not have hatched from their own eggs because they were added long before their own larvae hatched.
Abstract: Female burying beetles Necrophorus vespilloides Herbst (Coleoptera: Silphidae) were allowed to lay eggs on a carcass and their subsequent behavior towards larvae added to the carcass was observed. Females did not discriminate against unrelated larvae if these were added within an hour after the females' own first larva had hatched (at the “right” time). Changing the spatial surroundings of the carcass had no effect on the females' readiness to exhibit care behavior. Neither did the age of the larvae added or the condition of the carcass affect the onset of maternal care. However, the females' response to larvae encountered was strongly time-dependent: most females killed and ate larvae that could not have hatched from their own eggs because they were added long before their own larvae hatched. The proportion of females accepting larvae added “to early” increased as the time their own larvae hatched approached. Larvae added to the carcass 2 or 3 days after the test females' own first larva had hatched were always accepted by females that had already started to feed larvae, but were often killed by females that were not feeding larvae. In the latter group of females, the tendency to kill larvae added was most pronounced if the females had already started to produce a second clutch of eggs at the time larvae were added.
TL;DR: Differences in seasonal time of river ascent and descent, and instream behavior of adult wild and sea-ranched Atlantic salmon (Salmo salar) of the Norwegian River Imsa stock during the period 1981–1989 are documents.
Abstract: This paper documents differences in seasonal time of river ascent and descent, and instream behavior of adult wild and sea-ranched Atlantic salmon (Salmo salar) of the Norwegian River Imsa stock during the period 1981–1989. Wild fish use River Imsa as a nursery, and at an age of 2 years most of them migrate to the sea as smolts. The sea ranched fish are hatchery reared offspring of the River Imsa stock and are released as smolts at the mouth of the river. They are thus deprived of juvenile river life and a downstream smolt migration. Wild and sea ranched salmon feed for 1 or more years in the Norwegian Sea before homing as spawners. Both groups returned simultaneously to coastal Norway, but sea ranched fish ascended the river later and descended sooner after spawning than wild fish. All wild females and almost all wild males (96.2%) spawned in the river, whereas 13.5% and 36.7%, respectively, of the mature sea-ranched females and males left the river unspawned. The annual number, but not the proportion, of unspawned fish increased with increasing density of adult salmon in the river. Unspawned females were medium sized and small (45–70 cm); unspawned males were medium sized and large (50–90 cm). Independent of the density of spawners in the river, sea ranched fish moved up- and downstream the river more often than wild fish. More than 20% of the sea-ranched salmon and less than 1% of the wild salmon passed a trap 100 m above the river outlet more than once in each direction during the same spawning reason. Moreover, sea-ranched salmon were about twice as often seriously injured during spawning as wild fish. Lack of juvenile experience from the river may be the main reason for the behavioral differences between sea-ranched and wild fish.
TL;DR: Testing the fighting behaviour of male house mice when on a scent-marked substrate that matched the odour of an opponent with their behaviour on a substrate that did not match showed that the delay before the first fight was longer and the rate of subsequent fighting lower when the scents matched.
Abstract: If males assess potential opponents by comparing their odour with that of scent marks in the vicinity (the so called ‘scent matching’ hypothesis) they should be more reluctant to fight when these odours are the same. Under these circumstances the potential opponent is thus identified as a resource holder (a male monopolising a territory or group of females) that would escalate encounters to defend its resources. We tested this prediction by comparing the fighting behaviour of male house mice, Mus domesticus, when on a scent-marked substrate that matched the odour of an opponent with their behaviour on a substrate that did not match. As predicted, the delay before the first fight was longer and the rate of subsequent fighting lower when the scents matched. This result is consistent with the interpretation that resource holders scent mark to provide opponents with a means of competitor assessment and that they thus reduce the costs of resource defence.
TL;DR: The timing of feeding cessation coincided with that of scent-urination at both study sites, raising the possibility that appetite suppression may be a byproduct of physiological processes associated with chemical communication.
Abstract: Reduced forage intake by males is generally believed to coincide with the peak of rutting activities in many ungulates. Activity budgets of bull moose (Alces alces) in Denali National Park and Preserve (DNPP) and Isle Royale National Park (IRNP) were analyzed to assess: (1) if time spent foraging decreased during the rut; (2) the timing of reduced forage intake; (3) whether there was variation in feeding time among bulls of varying size; and (4) the proximate mechanism and adaptive value of reduced forage intake. Time spent feeding by bull moose began to decrease around 1 September: large bulls completely ceased feeding for approximately 2 weeks, with median dates of feeding cessation at 18 and 20 September for IRNP and DNPP, respectively. Small bulls fed at reduced rates, but did not cease feeding. Although large bulls in both study sites spent large amounts of time engaged in social behavior during the period of appetite suppression, much of their active time was also spent standing inattentive, i.e., engaged in no activity (45.5% in IRNP, 29.8% in DNPP), suggesting that a constraint in time budgets did not limit opportunities to feed. Forage intake reduction is more likely mediated through a physiological mechanism. Feeding cessation did not coincide with the peak of the rut: at DNPP the median date of feeding cessation was significantly earlier than the median date of breeding behavior and fighting. The timing of feeding cessation coincided with that of scent-urination at both study sites, raising the possibility that appetite suppression may be a byproduct of physiological processes associated with chemical communication.
TL;DR: Experimental and correlational data demonstrate that both the nutritional state of the male and his mate's fertility affect the timing and intensity of dawn and dusk song in the blackbird (Turdus merula).
Abstract: We present experimental and correlational data that demonstrate that both the nutritional state of the male and his mate's fertility affect the timing and intensity of dawn and dusk song in the blackbird (Turdus merula). Food supplementation leads to paired males singing earlier, for longer, and at higher peak rate at both dusk and dawn succeeding the treatment. We argue that the timing, not just the intensity, of song conveys information about the male's phenotypic condition. Both dawn and dusk song start earlier and have longer duration as a male's mate reaches peak fertility indicating that, in agreement with literature on the great tit (Parus major), song at this time has particular significance in mate guarding for paired males of monogamous species. We discuss the relative importance of these factors as functional explanations for the dawn chorus.
TL;DR: The results suggest that the cost of predation in unfamiliar areas may contribute to the evolution of philopatry in vervets, however, under unstable conditions, resource competition forces these animals to disperse (in groups) despite the high risk ofpredation.
Abstract: A decline in the density of trees and the deterioration of the habitat of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya, have been accompanied by movement of vervet groups into unfamiliar areas. These home range shifts were documented over a period of 26 months. The largest group moved into the home ranges of neighboring groups and acquired more trees, a resource that had become more limited. The groups whose home ranges were encroached upon did not share their home ranges with the intruders, but instead moved into areas that were unoccupied and had a lower density of trees. The largest group was thus more successful than smaller groups in competition for limited resources. For all but one group, movement into new areas was directly associated with the disappearances of female and immature monkeys. Most of the disappearances were attributable to predation. These results suggest that the cost of predation in unfamiliar areas may contribute to the evolution of philopatry in vervets. However, under unstable conditions, resource competition forces these animals to disperse (in groups) despite the high risk of predation.
TL;DR: Results of experimental introductions of parasites and a year of biweekly censuses at ten colonies indicate that leaf-cutting ants adjust the level of hitchhiking to accommodate both daily and seasonal changes in the abundance of parasites.
Abstract: A curious behavior in leaf-cutting ants in the genus Atta is the “hitchhiking” of small minim workers on leaf fragments carried by larger workers. Two functions of these hitchhikers have been proposed: (1) defense of leaf carriers against parasitic flies in the family Phoridae (ant protection hypothesis; Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967) and (2) reduction of transport costs of small minims that collect plant fluids (energy conservation hypothesis; Stradling 1978). We studied hitchhiking behavior in colonies of Atta colombica on Barro Colorado Island, Panama, and found strong evidence in favor of the ant protection hypothesis. Females of Apocephalus attophilus (Diptera: Phoridae) attack leaf carriers of A. colombica and deposit eggs in the head capsules of these ants. Our observations indicate that parasites require leaf fragments to stand on during oviposition, and, as a result, only leaf carriers are susceptible to parasitic attack. The presence of hitchhikers reduces significantly both the time parasites spend on leaf fragments and the probability that they will land in the first place. Results of experimental introductions of parasites and a year of biweekly censuses at ten colonies indicate that leaf-cutting ants adjust the level of hitchhiking to accommodate both daily and seasonal changes in the abundance of parasites. We found little evidence in support of the energy conservation hypothesis. If it is assumed that all minim workers hitchhike back to the nest, our calculations indicate that total transport costs along a foraging trail are reduced by 10% or less. However, our observations indicate that only 50% of returning minim workers hitchhike, and therefore energy savings are actually considerably less than 10%. Leaf-cutting ants in the genera Atta and Acromyrmex are attacked by over 20 species of parasitic phorids. In the discussion we review what is known about these associations and suggest that these parasites have influenced the ecology and evolution of polyethism in leaf-cutting ants.
TL;DR: Eagle prey selectivity by species generally supports the hypothesis that polyspecific associations among the monkeys are effective deterrents against predation.
Abstract: Results are presented from a 3.25-year study of a nesting pair of crowned hawk-eagles and an 18-year study of a primate community in the Kibale Forest, Uganda. The proportional composition of the living population of prey species was compared with that of eagle prey and animals dying from other causes. Monkeys were the predominant pry (83.7%). They also dominated the medium-to large-sized mammalian carcasses dying from other causes (88.9%). The eagles selected prey according to species, age, and sex. Selectivity by age and sex differed between prey species. Among red colobus monkeys, the eagles selected young juveniles and infants, but in four other monkey species they selected adult males. Eagle prey selectivity by species generally supports the hypothesis that polyspecific associations among the monkeys are effective deterrents against predation. The prey/predator ratio for the Kibale eagles was much higher, but the annual offtake of prey by the eagles was much lower than that of tropical felids. Mortality due to causes other than eagles was greater than expected in red colobus and less in redtails, but not significantly different from expected or equivocal in the other three monkey species. Other cause of mortality affected adult male and infant red colobus more than expected. Among the other four monkey species, significantly more adult males and fewer adult females died from these other causes than expected. Eagle predation had a major impact on the populations of adult males of both black and white colobus and blue monkeys and on both adult male and female mangabeys. The selectivity appeared to contribute significantly to the differential adult sex ratio in four monkey species, but not in red colobus. In contrast, mortality incurred during fighting among adult males probably accounted for the differential adult sex ratio in red colobus.
TL;DR: Among ungulates for which data are available, the best predictor of differential investment is not degree of adult sexual dimorphism; it is comparative rate of maternal investment.
Abstract: Prediction that mothers will invest more in individual sons than daughters in polygynous mammals has been confirmed in several species. However, among polygynous ungulates, differential investment occurs in some species, but not in others. Because ungulates have postnatal growth rates among the highest in mammals, we hypothesized that level of maternal investment limits the ability of offspring of one sex to evolve faster growth rates, even when intrasexual selection might favor faster growth. We predicted that comparative rate of maternal investment would explain the distribution of differential investment among ungulates, and examined our data on pronghorn (Antilocapra americana), which show the highest-known rate of maternal investment among ungulates. Data on birth weights, suckling rates, ages-pecific frequency of maternal termination of suckling bouts, age at weaning, and rate of rejected suckle attempts showed either no sex differences or else a slight excess investment in daughters. In concordance with these data, female fawns spent more energy in activity than did male fawns. Among ungulates for which data are available, the best predictor of differential investment is not degree of adult sexual dimorphism; it is comparative rate of maternal investment.
TL;DR: The optimal behavior during the breeding season must depend on prospects of survival, based both on maximal lifespan and vulnerability to predation, in the two marine gobiid fish species Pomatoschistus minutus and Gobius niger.
Abstract: In aquarium experiments, the two marine gobiid fish species Pomatoschistus minutus and Gobius niger were allowed to build nests and to spawn in the presence and absence of a predator (cod, Gadus morhua); behind a glass wall the predator was kept where it could be clearly seen by the gobies and vice versa. P. minutus showed no difference in number of nests or number of spawnings in the different treatments; approximately half of the males built nests, and the females spawned in half of those nests. G. niger, on the other hand, responded differently to the simulated predation risk. No nests were built in sight of the predator, whereas in the absence of predators, half of the males built nests and received eggs. The G. niger individuals in this experiment were 2–3 years old. However, when comparing the reproduction of G. niger of different age in the presence of a predator, older individuals (4–5 years) spawned, whereas younger (2–3 years) did not. No difference in vulnerability towards predators was found between equal-sized P. minutus and G. niger. The optimal behavior during the breeding season must depend on prospects of survival, based both on maximal lifespan and vulnerability to predation.
TL;DR: It is shown that behavioral differences in male investment in reproductive activities correlate with the potential for sperm competition.
Abstract: Data are presented on the breeding behavior of two zebra species to test whether intra- and interspecific variation in male reproductive behavior and physiology are correlated with differences in female promiscuity. In one species, plains zebra (Equus burchelli) females live in closed membership single male groups and mate monandrously. In the other species, the Grevy's zebra (E. grevyi) females live in groups whose membership is much more temporary. Typically, associations with individual males are brief and mating is polyandrous. However, some females - those having just given birth — reside with one male for long periods, mating monandrously. These differences in female mating behavior generate variability in the potential for sperm competition. We show that behavioral differences in male investment in reproductive activities correlate with the potential for sperm competition. When mating with promiscuous mares, Grevy's zebra stallions made a greater investment in reproductive behavior (calling, mounting, ejaculations) than did stallions of either species when mating with monandrous females. The evolution of large testes size in the Grevy's zebra, when compared to the congeneric plains zebra, horse, and mountain zebra, allows for this increased investment.