Showing papers in "Ethology Ecology & Evolution in 2011"
TL;DR: The role of predators in the evolution of defensive behaviours is still scarcely touched upon and this overview adds data to explore this and other evolutionary unsolved questions.
Abstract: Among vertebrates, defensive behaviours have been reviewed for fishes, salamanders, reptiles, birds, and mammals, but not yet for anuran amphibians. Although several defensive strategies have been reported for anurans, with a few exceptions these reports are limited in scope and scattered in the literature. This fact may be due to the lack of a comprehensive review on the defensive strategies of anurans, which could offer a basis for further studies and insights on the basic mechanisms that underlie these strategies, and thus lead to theoretical assumptions of their efficacy and evolution. Here we review the present knowledge on defensive behavioural tactics employed by anurans, add new data on already reported behaviours, describe new behaviours, and speculate about their origins. A total of 30 defensive behaviours (some with a few sub-categories) are here recognised. The terminology already adopted is here organised and some neologies are proposed. Some of the behaviours here treated seem to have an ind...
153 citations
TL;DR: Wolves in Italy seem to select wild ungulates over domestic ones where the former are available with rich and diversified guilds and abundant populations.
Abstract: We reviewed 20 studies on wolf diet in Italy, to relate the changes in diet composition to the increase of wild ungulate population in Italy. Researches covered the period from 1976 to 2004 and the whole range of wolves from southern Apennines to western Alps. We used the frequency of occurrence of seven food categories and of the wild ungulate species occurring in the diet. Estimates of wild ungulate populations were obtained from the literature and we extrapolated their trend in the period considered. Differences among geographic areas (south-central Apennines, northern Apennines, and western Alps) were tested by nonparametric multivariate analysis of variance, while the trends of the wild ungulate and livestock use and of diet breadth were analysed by regression and curve-fit analyses. We used the same method to support the relationships between the use and availability of wild ungulates. Wolves preyed on wild herbivores more in the northern Apennines and in the western Alps than in the southern Apenni...
81 citations
TL;DR: Noise and male density affected the song structure of great tits in urban habitats and it was found that males in noisier parks sang songs with higher minimum frequencies, more phrases and longer durations.
Abstract: Since ambient noise interferes with sound transmission, urban noise can affect the acoustic structure of birdsong. Previous studies have examined song features (e.g. high minimum frequency) in urbanised areas; however, these studies did not exclude the effects of other factors. For example, the intensity of male–male competition is known to affect song structure. In 22 urban parks in Tokyo, Japan, we measured the effects of noise level and male density, an indicator of the intensity of competition among males, and examined the relationship between these factors (noise and male density) and song structure of the great tit, Parus major. We found that males in noisier parks sang songs with higher minimum frequencies, more phrases and longer durations. The frequency shift appeared to mitigate the acoustic masking of songs by low-frequency background noise, as has been shown in previous studies. Songs with repeated phrases and of longer duration are likely to be more detectable for receivers under noisy condit...
60 citations
TL;DR: The finding of divergence in a set of traits probably related to mate recognition and choice is surprising within populations assigned to a single clade, and highlights the importance of considering behavioural traits in order to disentangle the evolutionary forces driving the diversification of A. femoralis.
Abstract: The identification of divergence in reproductive traits may substantially improve integrative approaches to understand species limits within clades that are suspected to contain cryptic diversity. The frog Allobates femoralis has been regarded as a pan-Amazonian species, and widely used as a model for addressing evolutionary issues regarding patterns of intraspecific diversification, social organisation, and animal communication. Recent accumulation of genetic, morphological, and bioacoustic data gathered from different localities strongly supports the idea that it represents a species complex, but field behavioural observations related to courtship and mating are surprisingly scarce. Here, we provide a description of several aspects of the reproductive biology of A. femoralis from a Central Amazon site, and compare our results with the few published reports for the species. This study demonstrated that, besides the known divergence in the number of notes of the A. femoralis call, there are both quantitat...
55 citations
TL;DR: It was shown that adult females had larger body size than males for all populations, and variation in body size in males did not change consistently with altitudes when removing the effect of age, not agreeing with Bergmann's rule.
Abstract: Identifying variations in morphology and age across geographical gradients may help us to understand the evolution of life-history of animals. In view of this, we studied variation in body size, age and growth of the Omei treefrog (Rhacophorus omeimontis) along altitudinal gradients in Baoxing County of Sichuan province in western China. The results showed that adult females had larger body size than males for all populations. Body size differed significantly among populations in males, but not in females. In three populations, the average age from the 760 m and 1690 m sites differed significantly between males and females, but not at the 1000 m site. Individuals from the 1690 m site exhibited delayed sexual maturity as well as having greater average age than those from the 1000 m and 760 m sites. For males, the growth rates declined with increasing altitudes, while females from the 1690 m site exhibited higher growth rates than their conspecifics from the 1000 m and 760 m sites. Variation in body size in...
41 citations
TL;DR: The tokay gecko complex has become differentiated geographically not only in terms of morphological characteristics but also in Terms of call acoustics.
Abstract: Geographic variations in vocalizations and morphological characteristics of the tokay gecko (Gekko gecko L.) complex were identified using subjects recorded and/or collected in China and Southeast Asia. Populations in south China and northeast Vietnam (the black tokay) were compared with those in Thailand, Laos and south Vietnam (the red tokay). Red tokays possess gray- or dark green-colored skin with brick red spots interspersed on the dorsum, while black tokays possess dark-green skin with black spots or spots of other colors except brick red. Each group produces advertisement calls which consist of distinct acoustic phases. In both groups the first call phase consists of a series of pulses and the second phase consists of a series of two-note syllables. Only red tokays produce a third phase consisting of single notes. Frequency modulation patterns were profoundly different for call elements produced between the two groups. Calls of the black but not red tokay exhibit intricate frequency modulated eleme...
34 citations
TL;DR: In this article, the authors described patterns and sex/age correlates of interspecific aggression between wild roe deer and fallow deer at feeding sites in Maremma Regional Park, central Italy.
Abstract: Information on interspecific aggression is scarce for wild ungulates. I described patterns and sex/age correlates of interspecific aggression between wild roe deer Capreolus capreolus and fallow deer Dama dama at feeding sites in Maremma Regional Park, central Italy. A previous study showed that fallow deer can actively exclude roe from feeding areas. Here I show that 81% out of 42 aggressive interactions were fallow–roe deer aggressions, whereas 19% were roe–fallow aggressions. No aggressive interaction involved physical contact between opponents and roe deer were displaced in all events. When roe deer avoided fallow deer, the probability of remaining feeding increased significantly with respect to when aggression occurred. Fallow deer males, especially yearlings, were more aggressive than females to all roe deer sexes/age classes. For fallow deer, aggression was an efficient way to monopolise the access to foraging space. For roe deer, spatial avoidance of fallow was a way to remain at feeding areas.
22 citations
TL;DR: The spatial distribution of the wolf spider Lycosa subfusca seems to be the result of the predation by tarantulas and conspecifics.
Abstract: In this work we studied the effect of size-dependent predation and cannibalism on the spatial distribution of the wolf spider Lycosa subfusca, which shares its habitat with a bigger spider: the tarantula Brachypelma vagans, in the Yucatan Peninsula. We examined (i) in the field, the predation interaction between medium tarantulas and large, medium and small wolf spiders; (ii) in the laboratory, size-dependent cannibalism in the wolf spider; and (iii) the simultaneous occurrence of small, medium and large tarantulas, and small, medium and large wolf spiders in three sites in the field (secondary forest, backyard and grazed lawn). In predation interactions, tarantulas attacked large wolf spiders more frequently than medium ones (55% vs 25%), and never attacked small ones. Cannibalism experiments in the wolf spider showed that attack was always initiated by the larger individual. Attack frequencies increased with spider size, but capture success was similar regardless of spider size. Medium and large wolf sp...
17 citations
TL;DR: It is documented that the time of emergence/activity in stylopised females follows the temporal trend of uninfected, protandrous males, and the potential adaptive value of the altered host behaviour for the parasite is ascribed to host manipulation.
Abstract: Stylopised (= parasitised by Strepsiptera Stylopidae) imagoes of Andrena (Hymenoptera Andrenidae) bees are known to exhibit intersexual morphology. Until now, their abnormal morphology has been thought to result from undernourishment of parasitised larvae during development. This hypothesis, however, dos not fit to mass provisioning Hymenoptera. We hypothesised that induced changes in the suite of morphological characters might be a consequence of manipulation of sex-specific behavioural traits by a strepsipteran parasite. Thus, the masculinised morphology of stylopised females might be connected with shifts in their sexual behaviour. Here, we tested the effect of Stylops (Strepsiptera Stylopidae) infection on the timing of spring nest emergence in Andrena bees, where males generally emerged conspicuously earlier than conspecific females. We used two independent data samplings – pan trapping and direct observation – to avoid possible bias caused by one of the methods. In accordance with our hypothesis, we...
17 citations
TL;DR: This is the first study to quantify the existence of a linear dominance hierarchy in male African elephants as well as the effect of climatic fluctuations on dominance from year to year.
Abstract: Linear dominance hierarchies are thought to form within groups of social animals to minimize conflict over access to resources. Dominance in both male and female African elephants (Loxodonta africana) is based mostly on intrinsic factors relating to age, and dominance hierarchies have been described within and between family groups of females. Very little is reported about male elephant social structure and dominance has only been described at the level of one-on-one contests. We test the hypothesis that male African elephants form linear hierarchies when resources are limited by monitoring a known group of elephants in Etosha National Park, Namibia, and measuring dominance interactions between males (outside the context of reproduction) during the dry season of 4 consecutive years. We show that males form a stable linear dominance hierarchy under normal arid conditions (in 2005 and 2007) when water is limited and resource competition is high. In unusually wet years with increased water availability (in 2...
16 citations
TL;DR: Social amoeba Dictyostelium discoideum was explored by forming chimeras between weakened cells and normal cells that were genetically identical, supporting the prediction of evolutionary conflict and indicating that there may also be an advantage in clonal groups to put strong cells in spores.
Abstract: When multicellularity originates through the aggregation of genetically variable cells, the interests of the component cells may conflict with each other. A prediction of conflict is that stronger cells will force weaker cells into non-reproductive tissues. However, if stronger cells are better in the reproductive tissues than in the somatic ones, then the same result may be expected in clonal organisms that optimize their development. We explored these issues in the social amoeba Dictyostelium discoideum by forming chimeras between weakened cells and normal cells that were genetically identical. We reduced the condition of amoebae (measured as increased doubling time) by growing them in media lacking glucose, or more acid than normal. Weakened cells were less competitive compared to healthy cells in becoming spore, supporting our prediction of evolutionary conflict. However, spores from weakened cells also proliferated slightly less rapidly than normal spores, indicating that there may also be an advanta...
TL;DR: Chemical defence in striped skunks may be more vital to the survival of juvenile skunks than adults that are capable of displaying the entire range of anti-predator behaviours, have greater experience, and potentially fewer predators.
Abstract: The defensive display of a threatened adult striped skunk (Mephitis mephitis) involves visual, auditory, and olfactory signals. Detection of a potential predator leads to either avoidance (run, hide, or den) or confrontational (tail-up, stomp, hiss, scratch, charge, aim, and spray) behaviours. Seventy skunks born in captivity were handled at five-day intervals starting at seven days of age and up to 52 days of age. The development of defensive behaviours (tail-up, stomp, run, aim, hide, spray, hiss, scratch, charge, and bite) and physical attributes (eye opening, external auditory meatus opening, and teeth eruption) were recorded. Tail-up, which signifies alertness and enhances warning colouration, was the most common and earliest defence behaviour observed. Musk was present at seven days of age, though the ability of a skunk to forcefully expel its chemical defence is not developed until 17 days. Initially spray events are not aimed at the threat; directed spray is initiated following eye opening at 32 d...
TL;DR: The authors' data showed significant differences in the nesting site microhabitat characteristics of two syntopic species of harvester ants partially due to a different capacity of the two species to alter nesting site proprieties.
Abstract: Physiological tolerance of species to temperature, moisture or chemical-physical properties of the soil could be important in determining the distribution and abundance of ant nests. In the present study we investigated the possible differences in the nesting site microhabitat characteristics of two syntopic species of harvester ants of the genus Messor living in a Mediterranean homogeneous grassland area belonging to a single phytosociological association known as “Vulpio ligusticae-Dasypyretum villosi”. We tested to see whether the activity of the colonies of the two species directly altered the microhabitat characteristics of the nesting sites. Microhabitat characteristics were assessed quantifying several abiotic factors (light, temperature, soil moisture, soil pH, nitrogen) by means of the Ellenberg Bioindication Model. The model represents a simple way of interpreting the vegetation pattern in terms of ecological factors from the perspective of the plants and can be considered an effective and promi...
TL;DR: The study indicates that it is blue-green, not the UV component of the egg's spectral characteristics, which seems to increase the perception of eggs by adults in dark cavities, which might have been the most important pressure towards evolution of blue- green colouration of eggs in cavity-nesting birds.
Abstract: We analysed the eggs of the European starling Sturnus vulgaris for variability of UV and blue-green colouration. We noted the calcium deposition in eggshells, egg measurements, light conditions in nests and starling eye properties. Egg colouration shows high within-clutch similarity. Intensity of the blue-green egg colour neither depends on Ca deposition in the eggshell nor correlates with egg measurements, clutch size and laying date. This suggests that the intensity of the blue-green colour of starling eggs does not reflect female condition, which is reported to affect egg and clutch parameters. Low light intensity in cavities enables only mesopic vision, which is characterised by degraded visual acuity and colour sense, as well as Purkinje shift. As a consequence, the probability of precise assessment of the differences in eggs colour by starling males, crucial for the signalling hypothesis (Moreno & Osorno 2003), is not high. On the other hand, irrespective of its intensity, blue-green is the last col...
TL;DR: It is found that the presence of major workers results in an increase in the movement of minors when gardens are infected with Escovopsis, suggesting that minor workers may be recruited to help defend the fungus garden from infection.
Abstract: Social insects that obligately depend on mutualists are known to defend both themselves and their partners from exploitation. One example is leaf-cutting ants, which defend the mutualistic fungus they cultivate for food from potentially virulent specialized microfungal parasites (genus Escovopsis). Mechanisms employed by the ants to reduce the impact of Escovopsis include grooming the mycelium of their fungal cultivar and weeding out infected parts of the fungus garden. These behavioral defense tasks are performed by specific size castes: minor and major workers, respectively. While minor workers are efficient at removing Escovopsis spores through fungus grooming, they are significantly less mobile than major workers. This implies that if major workers were to facilitate the movement of minor workers from uninfected to infected sites within colonies, defense against Escovopsis potentially would be faster, and consequently more efficient. Using dual-chamber sub-colony set-up experiments, we explore the rol...
TL;DR: It is shown that partner attractiveness may not influence the characteristics of egg quality, and that in this red-legged partridge species the females are able to invest in large clutches without a decrease of egg size but with a progressive decrease ofegg quality.
Abstract: In precocial bird species, the eggs represent a strong maternal allocation of resources and constitute most of the maternal investment since parents do not feed the young after they hatch. Females can differentially allocate resources in their eggs as a response to the environment experienced during the laying period, including the quality of their mate. To assess the importance of female selection on egg composition in the red-legged partridge, we tested breeding females in a choice trial in which they were allowed to choose between males. After the choice trials, the females were mated with their preferred male (P group), with a non-preferred one (NP group) or with a randomly selected male (RND group). Eggs laid by females of the three groups did not differ significantly in mass, shape, yolk, albumen or shell weight. Moreover, there was no significant difference in egg lysozyme concentration (an important albumen antimicrobial component). There was a significant difference in egg characteristics in relation to position in the laying order, with last-laid eggs being heavier and more spherical. Last-laid eggs contained more albumen but their shell was lighter and the albumen contained less lysozyme. This study shows that partner attractiveness may not influence the characteristics of egg quality, and that in this partridge species the females are able to invest in large clutches without a decrease of egg size but with a progressive decrease of egg quality.
TL;DR: Male treefrogs, to be sexually competitive, might mitigate vocal fatigue by modifying the call fine-scale structure but not the quantity of their calling, as with some marathon champions who change the techniquebut not the speed of their running to remain competitive in a race.
Abstract: We investigated the effects of within-night sustained calling on call acoustic properties in a typical lek-breeding anuran (Hyla intermedia), in which males engage in intense acoustic competitions to attract females. We continuously recorded the calling of randomly selected males over a large portion of the nightly chorus activity and investigated the pattern of temporal variation in both fine-scale (pulse rate, call duration and rise-time) and gross-scale (call rate, call-group duration) properties. Despite the strong within-individual correlations that we observed between both fine- and gross-scale properties, only the fine-scale properties showed a consistent pattern of temporal variation: during sustained calling, call duration and rise-time tended to increase and pulse rate to decrease, whereas call rate and call-group duration were as likely to decrease as to increase. We hypothesised that vocal fatigue from sustained calling was responsible for the observed pattern of within-night temporal variatio...
TL;DR: This study investigates the mechanisms that elicit a shift in search tactics using the frog D. muelleri and measures differences in the rate of the exploratory behaviours during the foraging activity.
Abstract: Search tactics are cognitive processes that organisms use to elicit a group of related and sequential behaviours that allow them to locate available resources Some species can modify their search tactics according to different ecological conditions, such as abundance and distribution of prey In this study, we investigate the mechanisms that elicit this shift in search tactics using the frog D muelleri as the subject of a laboratory experiment The shift in search tactics was measured by differences in the rate of the exploratory behaviours during the foraging activity Under experimental conditions, D muelleri alternates from sit-and-wait foraging when foraging within a patch, to widely foraging when locating prey aggregations The same behavioural response has also been observed in other animal groups (fishes and invertebrates), elicited by two ecological conditions, a shift in prey spatial distribution and a shift in prey abundance through time In general, when habitat components vary in time, caus
TL;DR: Prevalence and concordance of fungi in cloacae of pair members of a socially monogamous Arctic seabird, little auk (Alle alle), thereby testing whether the microbes are likely to be transmitted during copulation are determined.
Abstract: Sexually transmitted diseases have been frequently hypothesised as a cost of multiple avian mating but relatively few studies have investigated the issue in truly wild birds. The main object of this study was to determine prevalence and concordance of fungi in cloacae of pair members of a socially monogamous Arctic seabird, little auk (Alle alle), thereby testing whether the microbes are likely to be transmitted during copulation. Various fungi species, potentially pathogenic, occurred in the little auk cloacae. One-third of the tested individuals were found to be a host for one to three fungi species. However, half of the 19 studied pairs were found to be not concordant in fungal assemblages, suggesting that transmission of the microbes between partners is not straightforward.
TL;DR: Differences in variability that may be more difficult to detect than differences in acoustic properties per se are pointed to, and the effects of urbanisation on animal communication can be underestimated if inter-individual variation is not properly addressed.
Abstract: One of the clearest examples of animal adaptation to urban habitats is the variation in their vocalisations driven by anthropogenic noise. A behavioural process that has received less attention in urban habitats is how anthropogenic barriers influence animal spacing behaviour and communication. I addressed the effects of the distribution of bird territories in urban habitats and the pattern of song differentiation over distance among neighbouring birds. I studied natural and suburban populations of the white-crowned sparrow Zonotrichia capensis in Argentina. This songbird dwells in gardens, but is here less abundant and more regularly spaced than in open woodlands. Neighbouring birds in garden suburbs sang songs that were more similar to each other than neighbouring birds in natural habitats. Song differentiation was greater within natural habitats than within suburbs at distance < 400 m. At larger distances differences among habitats were no longer significant. Neighbour songs were more homogeneous where...
TL;DR: A detour problem combined with the classic delayed-response task, which has been extensively used to compare working memory duration in a variety of different species was employed to investigate location recall and search behaviour for a food target, after a short delay following its disappearance.
Abstract: In recent years, considerable literature has been published on cognition in horses; however, much less is known about the cognitive abilities of domestic donkey (Equus asinus). This study aimed to expand our knowledge of donkey cognition by assessing their short-term memory capacity. We employed a detour problem combined with the classic delayed-response task, which has been extensively used to compare working memory duration in a variety of different species. A two-point choice apparatus was used to investigate location recall and search behaviour for a food target, after a short delay following its disappearance. Four donkeys completed the task with a 10 sec delay, while four others were tested with a 30 sec delay. Overall, each group performed above chance level on the test, showing that subjects had successfully encoded, maintained, and retrieved the existence and location of the target despite the loss of visual contact.
TL;DR: Investigation of the influence of different plant material and mound size on insulation capacity and whether active heating owing to the fermentation process of the organic plant material does occur found that plant material seems to be important for temperature absorption capacity, although it is found no indication for insulation capacity.
Abstract: In contrast with house mice (Mus musculus musculus and Mus musculus domesticus), Mus spicilegus is seasonal in its reproduction. Thus overwinter survival seems to be an important factor for population dynamics. In autumn, the mice construct voluminous mounds made of plant material covered with soil, under which they overwinter without reproducing. These mounds could be used for food storage but a thermoregulatory function is a non-mutually exclusive explanation. In this study we investigated the influence of different plant material and mound size on insulation capacity and whether active heating owing to the fermentation process of the organic plant material does occur. We found no indication for active heating processes owing to fermentation but we did find that plant material seems to be important for temperature absorption capacity, although we found no indication for insulation capacity. Furthermore, mound size seems to have a significant effect on thermal stability.
TL;DR: The feeding rate by pecking was significantly higher in muddy soils when compared with either shallow water or rush beds and the lower feeding rate in rush beds, when compared to muddy soils, could be explained in terms of the spatial arrangement of this terrestrial substrate and, consequently, the higher level of predatory risk.
Abstract: We acquired data on diving times and feeding rates by pecking on three different substrates in a small wetland of central Italy, in order to improve the scant knowledge on foraging behaviour of the Eurasian coot (Fulica atra) in the Mediterranean area. Diving times showed a mean value of 2.59 sec (± 1.81 SD; n = 186). A large proportion of diving times (about 72%) were between 1 and 3 sec, a range corresponding to intrinsic physio-ecological times allowing a coot to search for food items below the water surface. The feeding rate by pecking was significantly higher in muddy soils when compared with either shallow water or rush beds. The data may be explainable in terms of the easier detectability and availability of different food items in muddy soils, which may increase the feeding rate by pecking on this substrate. The lower feeding rate in rush beds, when compared to muddy soils, could also be explained in terms of the spatial arrangement of this terrestrial substrate and, consequently, the higher level...
TL;DR: The results indicate that the beard length plays an important role in female choice in this species, as previously reported, and dominance status has a slight complementary effect.
Abstract: In many animal species ornaments and display behaviours are used together in intersexual communication. Few studies, however, have simultaneously explored how the static and dynamic components interact. We examined the significance of behaviour (e.g. dominance status) in comparison with beard length for the mate choice process in a bird species, the bearded reedling, Panurus biarmicus. In choice experiments, females were confronted with two males of varying beard length (artificially shortened or elongated) and status (dominant/subdominant). The results suggest that female choice is primarily based on beard length whereas dominance seems to be less important. Our results indicate that the beard length plays an important role in female choice in this species, as previously reported. Nevertheless, dominance status has a slight complementary effect. Beard length and behaviour seem to inform the female about the same aspect of male condition but with a different error probability. However, additional studies ...
TL;DR: Survition of yellow-legged gull chicks of either sex was differentially affected by maternal effects as mediated by hatching asynchrony, hatching order as well as egg mass, which constitute predictable gradients of pre- or post-natal environmental conditions potentially under parental control.
Abstract: Maternal effects may allow parents to increase their own fitness by adjusting progeny phenotype to pre- and post-natal conditions depending on the sex of individual offspring. In birds, sex-specific maternal effects can be mediated by predictable gradients of rearing conditions due to hatching asynchrony, egg laying date, order and mass, and brood sex ratio. In this study, we analysed the growth and survival consequences of experimentally reduced hatching asynchrony and order per se and in conjuction with other maternal effects (laying date, egg mass and sibling sex ratio) in yellow-legged gull (Larus michahellis) chicks of either sex. Survival of male chicks in synchronised broods was reduced compared to that of their sisters and that of male chicks in control broods, whereas survival of females but not that of males declined with hatching order independently of hatching synchronisation treatment. Survival of female but not male chicks declined with egg mass. In addition, survival of individual chicks, i...
TL;DR: Female tree sparrows adjusted their reproductive strategy over the course of the breeding season and invested the most resources in the second clutch, indicating that their decisions may serve to maximise the number of offspring they can successfully rear in a single breeding season.
Abstract: In order to evaluate how a multi-brooded bird species adapts its breeding strategy during the breeding season, we investigated variations in clutch size, egg traits and sex of the final eggs in a population of the tree sparrow Passer montanus in northwestern Croatia. Of the three clutches of the season, the second was the largest and it contained the largest eggs. Furthermore, the females followed the brood survivor strategy for the second clutch, while they chose the brood reduction strategy for the first and the third clutches. These results indicate that female tree sparrows adjusted their reproductive strategy over the course of the breeding season and invested the most resources in the second clutch. We hypothesise that their decisions may serve to maximise the number of offspring that they can successfully rear in a single breeding season.
TL;DR: Results of this study suggest that bluegill can adjust their reproductive activity by sensitively responding to the local temperature condition, probably contributing to the rapid expansion of the fish after introduction to the lake.
Abstract: The local difference in the ovary weight of bluegill Lepomis macrochirus was investigated in Lake Biwa, Japan. Fish samples were collected from four sites in May 2010 before the onset of spawning. Analytical results indicated that the ovary weights decreased significantly with latitude. The ratios of ovary weight to the body weight of fish collected at the lowest-latitude site frequently exceeded 10%, whereas those at the highest-latitude site were always below 5.79%. A latitudinal decrease in the ovary weight was obviously responsible for the higher body weights of fish in the south basin of the lake than those in the north basin, since the ovary-removed body weights of fish tended to increase with latitude. As the water temperature of Lake Biwa normally starts to increase in spring from lower latitudes, the latitudinal gradient in the ovary weight of bluegill appeared to be owing to the difference in the local temperature. Results of this study suggest that bluegill can adjust their reproductive activit...
TL;DR: It is proposed that temporal dependence among the length of inattentive periods in greater rheas would be the result of simple mechanistic rules determined by the compromise between foraging and scanning behaviour, and it would be of little value to potential stalking predators.
Abstract: Some models that predict the scanning pattern to maximise the probability of predator detection by prey assume sequential randomness (i.e. lengths of inter-scan intervals are independent of each other and of the length of scan events). Sequential randomness would prevent stalking predators synchronising their attacks with long inter-scan intervals. We analysed the presence of sequential randomness in the scanning behaviour of the greater rhea (Rhea americana), a large flightless bird that forages solitarily or in groups. We analysed sequences of behaviour of 40 wild rheas, foraging solitarily or in groups of 2 to 17 individuals, in two populations in eastern Argentina. We used parametric (auto and cross-correlations) and non-parametric (runs and Spearman rank correlation) tests to detect dependence among intervals. We detected the temporal dependence of inter-scan intervals in 30 of 40 behavioural series, but only 11 of 40 sequences showed consistent dependence when tested using parametric and non-paramet...
TL;DR: The findings pinpoint the vulnerability of nature reserves to species invasions, and call for more effective preventative measures.
Abstract: Since the nineteenth century, the mud snail Potamopyrgus antipodarum (Gray 1843), native to New Zealand, has been introduced into several European countries, Italy included. As a first step to contain its spread and establishment, it seems necessary to understand the characteristics of the environment that are more favourable for this species' invasion. To this aim, we analysed a number of physico-chemical and biotic parameters of four streams, two invaded and two not yet invaded, in the National Park of the Foreste Casentinesi, Monte Falterona, Campigna (Central Italy), where the species was first recorded in 2008. The two categories of streams, invaded and non-invaded, differ in only three of the 20 analysed characteristics of the habitat; that is, availability of crevices, width stream, and maximum water depth. This suggests that, despite P. antipodarum's documented tolerance to pollution, the high-quality waters of the park are highly susceptible to its invasion, if its vectors and pathways are not id...
TL;DR: It appears that the evolutionary loss of stalked migration gives D. discoideum cells the advantage of delaying specialization and the ability to colonize more distant locations, but has significant costs due to migration distance, such as the fraction of cells that become fertile spores.
Abstract: One of the challenges of microbial life is that the best location for feeding and growth may not be the best location for dispersal. This is likely to be the case for the social amoebae Dictyostelium discoideum and Dictyostelium purpureum that feed on soil bacteria in the amoeba stage, but then group into a multicellular slug that moves towards light before forming a fruiting body. Here we examine this short-range social dispersal in the social amoebae, Dictyostelium discoideum and D. purpureum. We predicted D. purpureum would have higher migration costs and travel less far because it forms a dead stalk from living cells as it moves, while D. discoideum delays stalk formation until movement ceases. We found that D. purpureum migrated shorter distances than D. discoideum, in accord with our prediction. D. discoideum slugs moved an average of 2.46 ± 0.19 cm while D. purpureum slugs moved an average of 1.04 ± 0.06 cm. In both species, migration incurred a cost in reduced spore production, compared to experim...