Biological Journal of the Linnean Society

BUTLER, RICHARD J.; BARRETT, PAUL M.; PENN, MALCOLM G.; KENRICK, PAUL

doi: 10.1111/j.1095-8312.2010.01401.xpmid: N/A

AbstractTesting coevolutionary scenarios over extended geological timescales is fraught with difficulties. Most tests rely on comparisons of temporal variations in taxonomic diversity for the groups of interest: however, this approach typically excludes spatiotemporal data. Here, we apply a quantitative method that incorporates the spatiotemporal distributions of the proposed coevolving groups using a Geographical Information System. Distributional data for Cretaceous dinosaur and plant groups were mapped onto palaeogeographical reconstructions in a series of time-slices. Within each time-slice, palaeocontinental surfaces were divided into a series of grids, each of which was scored as present, absent or inapplicable (unsampled) for each group. Distributions were compared statistically to determine whether the putative coevolving groups co-occurred within grid squares more or less frequently than expected by chance. Pairwise comparisons were made between herbivorous dinosaur clades and major plant groups (e.g. cycads, angiosperms) on a global scale. Only three nonrepeated associations of marginal significance were recovered, demonstrating that, in general, current knowledge of the spatiotemporal distributions of these groups provides little support for coevolutionary hypotheses. The Geographical Information System methods used are readily applicable to many other questions whose answers are reliant on a detailed knowledge of organismal distributions in time and space.

KOKSHENEV, VALERY B.; CHRISTIANSEN, PER

doi: 10.1111/j.1095-8312.2010.01415.xpmid: N/A

AbstractThe standard differential scaling of proportions in limb long bones (length against circumference) was applied to a phylogenetically wide sample of the Proboscidea, Elephantidae and the Asian (Elephas maximus) and African (Loxodonta africana) elephants. In order to investigate allometric patterns in proboscideans and terrestrial mammals with parasagittal limb kinematics, the computed slopes between long bone lengths and circumferences (slenderness exponents) were compared with published values for mammals, and studied within a framework of the theoretical models of long bone scaling under gravity and muscle forces. Limb bone allometry in E. maximus and the Elephantidae is congruent with adaptation to bending and/or torsion induced by muscular forces during fast locomotion, as in other mammals, whereas the limb bones in L. africana appear to be adapted for coping with the compressive forces of gravity. Hindlimb bones are therefore more compliant than forelimb bones, and the resultant limb compliance gradient in extinct and extant elephants, contrasting in sign to that of other mammals, is shown to be a new important locomotory constraint preventing elephants from achieving a full-body aerial phase during fast locomotion. Moreover, the limb bone pattern of African elephants, indicating a noncritical bone stress not increasing with increments in body weight, explains why their mean and maximal body masses are usually above those for Asian elephants. Differences in ecology may be responsible for the subtle differences observed in vivo between African and Asian elephants, but they appear to be more pronounced when revealed via mechanical patterns dictated by limb bone allometry.

CARLSON, ROSE L.; WAINWRIGHT, PETER C.

doi: 10.1111/j.1095-8312.2010.01417.xpmid: N/A

AbstractDarters are a species-rich radiation of small benthic and benthic-associated stream fishes that comprise approximately 20% of the diversity of the North American freshwater fish fauna. Here, we gather data from 165, or 87%, of described species and use this information to characterize the morphological diversity of the darter radiation. We focus on characters of the oral jaws known to function in prey capture and consumption in other perciform taxa in order to explicitly link morphological diversity to ecological diversity. In addition to a quantitative description of the morphospace occupied by darters, we identify several instances of significant morphological convergence. We also describe three groups of darter species that exhibit unusual jaw morphologies that are used in previously undescribed prey capture behaviours. Despite these new ecomorphs, we find that darters exhibit relatively low variation in trophic morphology when compared with two other radiations of teleost fishes, and that the observed variation is related more to differences in microhabitat use than to differences in prey type.

GRIFFITHS, DAVID

doi: 10.1111/j.1095-8312.2010.01404.xpmid: N/A

AbstractPublished species lists were analysed to determine the contributions of dispersal, habitat preference, river channel size, body size, and glacial history to large-scale patterns in freshwater fish species richness in North America, north of central Mexico. Total species richness declines to the north and west but the pattern for endemics differs from that of widespread species. Mississippi Basin regions are more species rich than more isolated, coastal, regions. Richness declines more rapidly with increasing latitude in riverine specialist than in habitat generalist species. Levels of endemism are greatest in species found in small- to medium-sized river channels. The strong Rapoport effect, more marked in migratory than resident species, is correlated with habitat preference, channel size, and glacial history. Body size increases with latitude, largely as a result of a trend from small resident to large migrant species. In unglaciated regions, ancestral species survived in large habitats because these are longer-lived, more extensive, less isolated and more stable than headwaters, permitting larger populations and lower extinction levels. Reduced levels of gene flow in small, peripheral, channels isolated by larger downstream habitats have resulted in the production of many, small range, small-bodied species. The latitudinal richness gradient is a consequence of speciation and extinction events in unglaciated faunas and an increasing domination of faunas by generalist, large bodied, large channel, recolonizing species in more northern regions.

REICHARD, MARTIN; POLAČIK, MATEJ

doi: 10.1111/j.1095-8312.2010.01406.xpmid: N/A

AbstractAllopatric populations separated by vicariance events are expected to evolve reproductive isolating mechanisms as a result of disparate selection pressures and genetic drift. The appearance of reproductive isolating mechanisms may vary across taxa with differences in the opportunity for mate choice, and may be asymmetrical. In addition, premating barriers may be affected by individual mating experience. We used choice and no-choice experiments to investigate reproductive isolation between two allopatric (island and mainland) and colour-differentiated populations of an African annual fish, Nothobranchius korthausae. Assortative mating under experimental conditions was limited and asymmetrical. Preference for sympatric males was only expressed in nonvirgin females from one population. Virgin fish from both populations mated indiscriminately. No difference in the number of eggs laid, fertilization rate and hatching success was detected in no-choice experiments. All mating combinations produced viable offspring and no postmating barriers were detected in terms of the performance and fertility of F1 hybrids. Overall, we found little evidence for significant reproductive isolation, which is in contrast with the related killifish taxa in which assortative mating can be strong, even among allopatric populations with no colour differentiation.

MARTIN, RYAN A.; PFENNIG, DAVID W.

doi: 10.1111/j.1095-8312.2010.01380.xpmid: N/A

AbstractResource polymorphism – the occurrence within a single population of discrete intraspecific morphs showing differential resource use – has long been viewed as an important setting for evolutionary innovation and diversification. Yet, relatively few studies have evaluated the ecological factors that favour resource polymorphism. Here, we combine observations of natural populations with a controlled experiment to assess the role of intraspecific competition (specifically, the density of conspecifics) and ecological opportunity (specifically, the range of resources available) on the expression of resource polymorphism in spadefoot toad tadpoles. We found that greater conspecific densities and a greater range of available resources together promoted the expression of resource polymorphism. We conclude that, ecological opportunity, in the form of diverse available resources, along with intraspecific competition, may be a prerequisite for resource polymorphism to evolve, because such polymorphisms require diverse resources onto which each morph can specialize as an adaptive response to minimize competition.

ROBBINS, TRAVIS R.; WARNER, DANIEL A.

doi: 10.1111/j.1095-8312.2010.01429.xpmid: N/A

AbstractFew studies have collected longitudinal data that follow the complete microevolutionary path of an organism linking sources of variation (e.g. environmental versus genetic) to a trait and its subsequent relationship with fitness. Identifying the links within this pathway is imperative for understanding the ecological relevance of effects found at the phenotypic level. Furthermore, experimental studies that examine parts of the pathway in ectothermic organisms often fail to mimic the complexities of the natural developmental environment. Temperature and moisture conditions in reptile nests, for example, can fluctuate greatly on a seasonal and daily basis. Despite the potential effects of fluctuating environments, the vast majority of studies have held environmental treatments constant during the developmental period. We investigated the effects of fluctuating moisture regimes during incubation on eggs, hatchling phenotypes, and subsequent survival in the eastern fence lizard Sceloporus undulatus. Moisture fluctuations during embryonic development caused water absorption by eggs to follow the environmental availability of moisture. Initial hatchling tail length was affected by the pattern of moisture fluctuations, and hatchling growth rates in fluctuating treatments were significantly faster than those in a constant treatment, resulting in larger hatchlings after 4 weeks. A release–recapture experiment conducted in the field did not detect a treatment effect on survival despite the larger body sizes. In summary, although fluctuations affected water absorption by eggs and some hatchling traits, these effects did not have subsequent fitness consequences. The results obtained suggest that egg and hatchling survival are buffered against natural soil moisture fluctuations during incubation, even when egg and hatchling traits are significantly affected.

TALLOEN, WILLEM; LENS, LUC; VAN DONGEN, STEFAN; ADRIAENSEN, FRANK; MATTHYSEN, ERIK

doi: 10.1111/j.1095-8312.2010.01422.xpmid: N/A

AbstractConditions experienced during early development may affect both adult phenotype and performance later during life. Phenotypic traits may hence be used to indicate past growing conditions and predict future survival probabilities. Relationships between phenotypic markers and future survival are, however, highly heterogeneous, possibly because poor- and high-quality individuals cannot be morphologically discriminated when developing under good environmental conditions. Sub-optimal breeding conditions, in contrast, may unmask poor-quality individuals in a measurable way at the morphological level. We thus predict stronger associations between phenotype and performance under stress. In this field study, we test this hypothesis, experimentally challenging the homeostasis of great tit (Parus major) nestlings by short-term deprivation of parental care, which had no immediate effect on nestling fitness. The experiment was replicated during two subsequent breeding seasons with contrasting ambient weather conditions. Experimental (short-term) stress affected tarsus growth but not residual mass at fledging, whereas ambient (continuous) stress affected residual mass but not tarsus growth. Short-term stress effects on tarsus length and tarsus fluctuating asymmetry were only apparent when ambient conditions were unfavourable. Residual mass and hatching date, but none of the other phenotypic traits, predicted local survival, whereby the strength of the relationship did not vary between both years. Because effects of stress on developmental homeostasis are likely to be trait-specific and condition-dependent, studies on the use of phenotypic markers for individual fitness should integrate multiple traits comprising different levels of developmental complexity.

SHULTZ, SUSANNE; DUNBAR, ROBIN I. M.

doi: 10.1111/j.1095-8312.2010.01427.xpmid: N/A

AbstractIn birds, large brains are associated with a series of population-level phenomena, including invasion success, species richness, and resilience to population decline. Thus, they appear to open up adaptive opportunities through flexibility in foraging and anti-predator behaviour. The evolutionary pathway leading to large brain size has received less attention than behavioural and ecological correlates. Using a comparative approach, we show that, independent of previously recognized associations with developmental constraints, relative brain size in birds is strongly related to biparental care, pair-bonding, and stable social relationships. We also demonstrate correlated evolution between large relative brain size and altricial development, and that the evolution of both traits is contingent on biparental care. Thus, biparental care facilitates altricial development, which permits the evolution of large relative brain size. Finally, we show that large relative brain size is associated with pair-bond strength, itself a likely consequence of cooperation and negotiation between partners under high levels of parental investment. These analyses provide an evolutionary model for the evolution of and prevalence of biparental care, altricial development, and pair-bonding in birds.

WEIGEND, MAXIMILIAN; ACKERMANN, MARKUS; HENNING, TILO

doi: 10.1111/j.1095-8312.2010.01419.xpmid: N/A

AbstractReward partitioning and replenishment and specific mechanisms for pollen presentation are all geared towards the maximization of the number of effective pollinator visits to individual flowers. An extreme case of an apparently highly specialized plant–pollinator interaction with thigmonastic pollen presentation has been described for the morphologically complex tilt-revolver flowers of Caiophora arechavaletae (Loasaceae) pollinated by oligolectic Bicolletes pampeana (Colletidae, Hymenoptera). We studied the floral biology of Nasa macrothyrsa (Loasaceae) in the field and in the glasshouse, which has very similar floral morphology, but is pollinated by polylectic Neoxylocopa bees (Apidae, Hymenoptera). We investigated the presence of thigmonastic anther presentation, visitor behaviour (pollinators and nectar robbers), co-ordination of pollinator visits with flower behaviour and the presence of nectar replenishment. The aim of this study was to understand whether complex flower morphology and behaviour can be explained by a specialized pollination syndrome, or whether alternative explanations can be offered. The results showed that Nasa macrothyrsa has thigmonastic pollen presentation, i.e. new pollen is rapidly (<< 10 min) presented after a pollinator visit. Nectar secretion is independent of removal and averages 7–14 µL h–1. The complex flowers, however, fail to exclude either native (hummingbirds) or introduced (honeybees) nectar robbers, nor does polylectic Neoxylocopa actively collect the pollen presented. The findings do not support a causal link between complex flower morphology and functionality in Loasaceae and a highly specialized pollination. Rapid pollen presentation is best explained by the pollen presentation theory: the large proportion of pollinators coming shortly after a previous visit find little nectar and are more likely to move on to a different plant. The rapid presentation of pollen ensures that all these valuable ‘hungry pollinators’ are dusted with small pollen loads, thus increasing the male fitness of the plant by increasing the likelihood of siring outcrossed offspring.