Evolutionary history shapes the association between developmental instability and population‐level genetic variation in three‐spined sticklebacks

Developmental instability (DI) is the sensitivity of a developing trait to random noise and can be measured by degrees of directionally random asymmetry [fluctuating asymmetry (FA)]. FA has been shown to increase with loss of genetic variation and inbreeding as measures of genetic stress, but associations vary among studies. Directional selection and evolutionary change of traits have been hypothesized to increase the average levels of FA of these traits and to increase the association strength between FA and population‐level genetic variation. We test these two hypotheses in three‐spined stickleback (Gasterosteus aculeatus L.) populations that recently colonized the freshwater habitat. Some traits, like lateral bone plates, length of the pelvic spine, frontal gill rakers and eye size, evolved in response to selection regimes during colonization. Other traits, like distal gill rakers and number of pelvic fin rays, did not show such phenotypic shifts. Contrary to a priori predictions, average FA did not systematically increase in traits that were under presumed directional selection, and the increases observed in a few traits were likely to be attributable to other factors. However, traits under directional selection did show a weak but significantly stronger negative association between FA and selectively neutral genetic variation at the population level compared with the traits that did not show an evolutionary change during colonization. These results support our second prediction, providing evidence that selection history can shape associations between DI and population‐level genetic variation at neutral markers, which potentially reflect genetic stress. We argue that this might explain at least some of the observed heterogeneities in the patterns of asymmetry.     

Structure and diversity of the Mesozoic wood genus Xenoxylon in Far East Asia: implications for terrestrial palaeoclimates

Although the faunal elements of Far East Asian Mesozoic terrestrial biota have attracted much attention in recent years, their palaeoecology remains poorly known. In particular, features of the palaeoclimate are highly controversial. To address this point we used the Mesozoic fossil wood Xenoxylon , a genus recognized as an indicator of wet temperate biotopes and which is common in the area during the Carnian–Maastrichtian interval. We re-appraised bibliographic data and gathered new data for Xenoxylon in the Mesozoic of Far East Asia. This demonstrated that previous taxonomic approaches to the genus have been so far idiosyncratic. We examined the anatomical diversity of morphogenus Xenoxylon in Far East Asia and compared it to that of samples from Europe. This indicates that in an area centred on north-eastern China, Xenoxylon reached a level of anatomical diversity unmatched elsewhere in the world. We hypothesize that this diversity witnesses the persistence of palaeoecological conditions particularly suitable for Xenoxylon and that a wet temperate climate prevailed over most of the area throughout the Carnian–Maastrichtian interval. It is in this setting that the famous Jehol Biota probably evolved.     

Repeatability of dispersal behaviour in a common dwarf spider: evidence for different mechanisms behind short‐ and long‐distance dispersal

Abstract 1. The response of dispersal towards evolution largely depends on its heritability for which upper limits are determined by the trait’s repeatability. 2. In the Linyphiid spider E. atra, we were able to separate long‐ and short‐distance dispersal behaviours (respectively ballooning and rappelling) under laboratory conditions. By performing repeated behavioural trials for females, we show that average dispersal trait values decrease with increasing testing days. By comparing mated and unmated individuals during two periods (before and after mating for the mated group, and the same two periods for the unmated group), we show that mating has no effect on the mean displayed dispersal behaviour or its within‐individual variation. Repeatabilities were high and consistent for ballooning motivation, but not for rappelling. 3. Ballooning motivation can be regarded as highly individual‐specific behaviour, while general pre‐dispersal and rappelling behaviours showed more individual variation. Such difference in repeatability between long‐ and short‐distance dispersal suggests that short‐ and long‐distance dispersal events are triggered by different ecological and evolutionary mechanisms.     

Relationships between bird morphology and prey selection in two sympatric Great Cormorant Phalacrocorax carbo subspecies during winter

Variation in bird morphology (notably sex size dimorphism) has been suggested to contribute to differences in food use between individuals. We explore the hypothesis of food partitioning (diet overlap and prey size selection) in two sympatric subspecies of the Great Cormorant Phalacrocorax carbo with respect to bird morphology (subspecies and sex) in inland French waters. These areas represent a recent and increasing contact zone used as a common non-territorial winter feeding area by the continental P. c. sinensis and the marine P. c. carbo subspecies. A high dietary overlap between subspecies and sexes was found at the major sites studied. Prey size selection was found to be site-specific and generally related to a gradient of structural size and body mass (male P. c. carbo  > male P. c. sinensis  > female P. c. carbo  > female P. c. sinensis ). With respect to bird morphology, differences in prey size consumed by Great Cormorants were more pronounced between sexes in freshwater habitats than between subspecies. This was reinforced by the fact that P. c. carbo birds entering inland areas were smaller than birds on the coast. These results also suggest that bird morphology is an important determinant of dietary differences. Our study demonstrated that P. c. carbo is an efficient generalist forager in continental areas, and food partitioning in type and size of prey between the two subspecies is low.