Showing papers by "Roger K. Butlin published in 2003"

Understanding and confronting species uncertainty in biology and conservation

Abstract: Recent essays on the species problem have emphasized the commonality that many species concepts have with basic evolutionary theory. Although true, such consensus fails to address the nature of the ambiguity that is associated with species-related research. We argue that biologists who endure the species problem can benefit from a synthesis in which individual taxonomic species are used as hypotheses of evolutionary entities. We discuss two sources of species uncertainty: one that is a semantic confusion, and a second that is caused by the inherent uncertainty of evolutionary entities. The former can be dispelled with careful communication, whereas the latter is a conventional scientific uncertainty that can only be mitigated by research. This scientific uncertainty cannot be ‘solved’ or stamped out, but neither need it be ignored or feared. For researchers, few ideals are as sought after as those of the independent observer; preferably, a scientist should discover and transmit his or her story, and not be a part of it. But what if that cannot be arranged? In some fields, most notably quantum physics and human behavioral research, observation per se can have a direct effect on outcomes, so that studies must be designed to incorporate those effects. Of course, research in these fields does not come to a halt. Neither does research halt in other fields where the impact of the observer cannot be avoided or ignored safely, but rather is addressed directly as part of the research program. Here, we argue that biological research on species will benefit from an explicit recognition of the inherent limitations that biologists experience as investigators of species.

Inter and intra-population variation in shoaling and boldness in the zebrafish (Danio rerio)

Abstract: Population differences in anti-predator behaviour have been demonstrated in several species, although less is known about the genetic basis of these traits. To determine the extent of genetic differences in boldness (defined as exploration of a novel object) and shoaling within and between zebrafish (Danio rerio) populations, and to examine the genetic basis of shoaling behaviour in general, we carried out a study that involved laboratory-raised fish derived from four wild-caught populations. Controlling for differences in rearing environment, significant inter-population differences were found in boldness but not shoaling. A larger shoaling experiment was also performed using one of the populations as the basis of a North Carolina type II breeding design (174 fish in total) to estimate heritability of shoaling tendency. A narrow-sense heritability estimate of 0.40 was obtained, with no apparent dominance effects.

Inter and intra-population variation in shoaling and boldness in the zebrafish (Danio rerio)

Abstract: Population differences in anti-predator behaviour have been demonstrated in several species, although less is known about the genetic basis of these traits. To determine the extent of genetic differences in boldness (defined as exploration of a novel object) and shoaling within and between zebrafish (Danio rerio) populations, and to examine the genetic basis of shoaling behaviour in general, we carried out a study that involved laboratory-raised fish derived from four wild-caught populations. Controlling for differences in rearing environment, significant inter-population differences were found in boldness but not shoaling. A larger shoaling experiment was also performed using one of the populations as the basis of a North Carolina type II breeding design (174 fish in total) to estimate heritability of shoaling tendency. A narrow-sense heritability estimate of 0.40 was obtained, with no apparent dominance effects.

Evolution in the slow lane: molecular rates of evolution in sexual and asexual ostracods (Crustacea: Ostracoda)

Abstract: Parthenogenetic lineages within non-marine ostracods can occur either in mixed (with sexual and asexual females) or exclusively asexual taxa. The former mode of reproduction is associated with a high intraspecific diversity at all levels (genetic, morphological, ecological) and, at least in the Cypridoidea, with geographical parthenogenesis. Obligate asexuality is restricted to the Darwinuloidea, the strongest candidate for an ancient asexual animal group after the bdelloid rotifers, and is characterized by low diversity. We have compared rates of molecular evolution for the nuclear ITS1 region and the mitochondrial COI gene amongst the three major lineages of non-marine ostracods with sexual, mixed and asexual reproduction. Absolute rates of molecular evolution are low for both regions in the darwinulids. The slow-down of evolution in ITS1 that has been observed for Darwinula stevensoni (Brady & Robertson) apparently does not occur in other darwinulid species. ITS1 evolves more slowly than COI within non-marine ostracod families, including the darwinulids, but not between superfamilies. The ancient asexuals might have a higher relative substitution rate in ITS1, as would be expected from hypotheses that predict the accumulation of mutations in asexuals. However, the speed-up of ITS could also be ancient, for example through the stochastic loss of most lineages within the superfamily after the Permian-Triassic mass extinction. In this case, the difference in rate would have occurred independently from any effects of asexual reproduction.

Premating barriers to gene exchange and their implications for the structure of a mosaic hybrid zone between Chorthippus brunneus and C. jacobsi (Orthoptera: Acrididae).

Abstract: Many hybrid zones contain a deficit of hybrid genotypes relative to expectations from tension zone models This is often associated with separation of parental genotypes into distinct habitats (mosaicism), but sometimes parentals can be found co-occuring in the same local population (bimodality) In both cases, prezygotic isolation may play an important role in determining the genotypic composition of the zone Chorthippus brunneus and C jacobsi (Orthoptera: Acrididae) meet and form a complex hybrid zone in northern Spain Analysis of stridulatory peg numbers reveals partial spatial and seasonal isolation in a 25 km 2 area of the zone: C jacobsi phenotypes predominate in June and July and are present in both valley and mountain habitats; C brunneus phenotypes predominate in August and are restricted to valley habitats, always in sympatry with C jacobsi Strong assortative mating was observed in laboratory mating experiments Spatial, seasonal and behavioural isolation combine to produce strong premating isolation in the study area These results suggest a role for premating isolation in maintaining both the mosaic structure and bimodality of this hybrid zone

Molecular phylogenetics of the Oriental members of the Myzomyia Series of Anopheles subgenus Cellia (Diptera: Culicidae) inferred from nuclear and mitochondrial DNA sequences

Abstract: . The phylogenetic relationships of fifteen Oriental and two Afrotropical taxa of the Myzomyia Series of Anopheles subgenus Cellia and two outgroup species, An. maculatus (Neocellia Series) and An. dirus A (Neomyzomyia Series), were inferred from nucleotide sequences of the entire 685 bp of the mitochondrial cytochrome oxidase subunit II locus (COII) and 372 bp of the third domain (D3) of the 28S rDNA locus, both separately and together. Alignment of the D3 sequences was achieved with the aid of secondary structure comparisons, and the pattern of nucleotide substitution was best explained by the GTR + I + G model for either separate or combined datasets. Maximum likelihood and maximum parsimony analyses robustly identified five monophylies: An. fluviatilis U and T; An. fluviatilis U and T + An. minimus A, C, E and #157 + An. leesoni; An. filipinae + An. mangyanus; An. filipinae + An. mangyanus + An. aconitus; and An. culicifacies A and B. The results confirm the specific status of An. flavirostris, the close relationship of An. leesoni with the Minimus Complex, and the exclusion of An. jeyporiensis, An. culicifacies s.l and An. funestus from the Minimus Group. All of the species classified as members of the Minimus Group on morphological grounds formed a single clade, which comprised two subgroups: the Minimus Subgroup, including An. minimus s.l., An. fluviatilis s.l., An. leesoni and An. flavirostris, and the Aconitus Subgroup, including An. filipinae, An. mangyanus, An. aconitus, An. pampanai and An. varuna. However, these clades are only weakly supported by the present dataset.

Transitions in cuticular composition across a hybrid zone: historical accident or environmental adaptation?

Abstract: Two subspecies of the grasshopper Chorthippus parallelus form a hybrid zone in the Pyrenees. Transitions across the zone, including changes in mating signals and reproductive isolation have been intensively studied. Cuticular pheromones have been identified as likely mate recognition signals. Since the major role of the cuticle is in waterproofing, environmental adaptation of cuticular composition has the interesting potential to generate assortative mating as an incidental by-product. We describe the pattern of variation in cuticular hydrocarbon blend in four transects through the hybrid zone. We find no evidence for a previously observed displaced cline in one blend component. There were differences between subspecies but these varied among transects and were small compared with variation between transects. We examined environmental variation within one transect and found a correlation between vegetation and cuticular composition, suggesting that environment influences the constitution of the cuticle, and hence natural selection may interact with mating signals in this species. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78, 193−201.

Measuring dispersal and detecting departures from a random walk model in a grasshopper hybrid zone

Abstract: . 1. The grasshopper species Chorthippus brunneus and C. jacobsi form a complex mosaic hybrid zone in northern Spain. Two mark–release–recapture studies were carried out near the centre of the zone in order to make direct estimates of lifetime dispersal. 2. A model framework based on a simple random walk in homogeneous habitat was extended to include the estimation of philopatry and flying propensity. Each model was compared with the real data, correcting for spatial and temporal biases in the data sets. 3. All four data sets (males and females at each site) deviated significantly from a random walk. Three of the data sets showed strong philopatry and three had a long dispersal tail, indicating a low propensity to move further than predicted by the random walk model. 4. Neighbourhood size estimates were 76 and 227 for the two sites. These estimates may underestimate effective population size, which could be increased by the long tail to the dispersal function. The random walk model overestimates lifetime dispersal and hence the minimum spatial scale of adaptation. 5. Best estimates of lifetime dispersal distance of 7–33 m per generation were considerably lower than a previous indirect estimate of 1344 m per generation. This discrepancy could be influenced by prezygotic isolation, an inherent by-product of mosaic hybrid zone structure.