Altitudinal migration: ecological drivers,knowledge gaps,and conservation implications

Animal migration has been the subject of intensive research for more than a century, but most research has focused on long‐distance rather than short‐distance migration. Altitudinal migration is a form of short‐distance migration in which individuals perform seasonal elevational movements. Despite its geographic and taxonomic ubiquity, there is relatively little information about the intrinsic and extrinsic factors that influence altitudinal migratory behaviour. Without this information, it is difficult to predict how rapid environmental changes will affect population viability of altitudinal migrants. To synthesize current knowledge, we compiled literature on altitudinal migration for all studied taxa, and identified the leading hypotheses explaining this behaviour. Studies of animal altitudinal migration cover many taxonomic lineages, with birds being the most commonly studied group. Altitudinal migration occurs in all continents except for Antarctica, but about a third of the literature focused on altitudinal migration in North America. Most research suggests that food and weather are the primary extrinsic drivers of altitudinal migration. In addition, substantial individual‐level variation in migratory propensity exists. Individual characteristics that are associated with sex, dominance rank, and body size explain much of the variation in migratory propensity in partially migratory populations, but individual‐level correlates are poorly known for most taxa. More research is needed to quantify the effects of habitat loss, habitat fragmentation, and climate change on altitudinal migrants. Demographic studies of individually marked populations would be particularly valuable for advancing knowledge of the cascading effects of environmental change on migratory propensity, movement patterns, and population viability. We conclude our review with recommendations for study designs and modelling approaches that could be used to narrow existing knowledge gaps, which currently hinder effective conservation of altitudinal migratory species.     

Global drivers of population density in terrestrial vertebrates

Aim

Although the effects of life history traits on population density have been investigated widely, how spatial environmental variation influences population density for a large range of organisms and at a broad spatial scale is poorly known. Filling this knowledge gap is crucial for global species management and conservation planning and to understand the potential impact of environmental changes on multiple species.

Location

Global.

Time period

Present.

Major taxa studied

Terrestrial amphibians, reptiles, birds and mammals.

Methods

We collected population density estimates for a range of terrestrial vertebrates, including 364 estimates for amphibians, 850 for reptiles, 5,667 for birds and 7,651 for mammals. We contrasted the importance of life history traits and environmental predictors using mixed models and tested different hypotheses to explain the variation in population density for the four groups. We assessed the predictive accuracy of models through cross‐validation and mapped the partial response of vertebrate population density to environmental variables globally.

Results

Amphibians were more abundant in wet areas with high productivity levels, whereas reptiles showed relatively higher densities in arid areas with low productivity and stable temperatures. The density of birds and mammals was typically high in temperate wet areas with intermediate levels of productivity. The models showed good predictive abilities, with pseudo‐R² ranging between 0.68 (birds) and 0.83 (reptiles).

Main conclusions

Traits determine most of the variation in population density across species, whereas environmental conditions explain the intraspecific variation across populations. Species traits, resource availability and climatic stability have a different influence on the population density of the four groups. These models can be used to predict the average species population density over large areas and be used to explore macroecological patterns and inform conservation analyses.     

Sites of cell proliferation during scute morphogenesis in turtle and alligator are different from those of lepidosaurian scales

Cell proliferation in forming shield scutes has been studied by immunofluorescence in embryos of turtle, alligator and snake after injection of 5‐bromo‐deoxy‐uridine. Hinge regions of scutes in alligator and turtle carapace derive from an initial waving and invagination of the epidermis that contains 5‐bromo‐deoxy‐uridine‐labelled cells. This suggests that down growth of the epidermis into the dermis is driven by local proliferation in addition to dermal anchorage and stabilization of hinge regions. Few keratinocytes migrate into suprabasal layers 1 day after injection of 5‐bromo‐deoxy‐uridine and keratinocytes reach the precorneous layer in about 5 days. Proliferating keratinocytes are randomly distributed in the outer scale surface of symmetric scutes but are more numerous in the outer scale surface of asymmetric or overlapped scutes indicating epidermal expansion. Higher localization of proliferating cells along hinge regions of embryonic turtle and alligator scutes is maintained in adult scutes where most growth occurs. In snake, skin proliferation becomes prevalent on the elongating outer side of the asymmetric scale. Comparison between proliferation sites in turtle–alligator–chick scales with lepidosaurian scales indicates that placodes are present only in turtle–alligator–chick scales. Conversely, scale primordia detected only using gene markers are found in most crocodilian and lepidosaurians embryonic skin.     

Conservation of sex chromosomes in lacertid lizards

Sex chromosomes are believed to be stable in endotherms, but young and evolutionary unstable in most ectothermic vertebrates. Within lacertids, the widely radiated lizard group , sex chromosomes have been reported to vary in morphology and heterochromatinization, which may suggest turnovers during the evolution of the group. We compared the partial gene content of the Z‐specific part of sex chromosomes across major lineages of lacertids and discovered a strong evolutionary stability of sex chromosomes. We can conclude that the common ancestor of lacertids, living around 70 million years ago (Mya), already had the same highly differentiated sex chromosomes. Molecular data demonstrating an evolutionary conservation of sex chromosomes have also been documented for iguanas and caenophidian snakes. It seems that differences in the evolutionary conservation of sex chromosomes in vertebrates do not reflect the distinction between endotherms and ectotherms, but rather between amniotes and anamniotes, or generally, the differences in the life history of particular lineages.     

Male mating success in a North American pitviper: influence of body size,testosterone, and spatial metrics

Males with enhanced traits relative to conspecifics often show increased mating and reproductive success and thus have a fitness advantage. The opportunity or potential for sexual selection is predicted to occur under these conditions. Here, we investigated proximate determinants of mating success in male copperhead snakes (Agkistrodon contortrix), a medium‐sized pitviper of North America. Specifically, we investigated the relationships of body size (snout‐vent length, body mass), body condition index, spatial metrics (total distance moved, home range size), and plasma testosterone concentration on mating success in males. The single mating season lasts from August through September. We compared a set of candidate linear mixed models and selected the best‐fitting one using the adjusted Akaike Information Criterion (AICc). The AICc‐selected model (model 2), with testosterone, body condition index, and home range size as predictor variables, showed that male mating success was positively correlated with testosterone. To our knowledge, this is the first report to show the relationship of testosterone and individual mating success in any snake species. A parallel study conducted on male fitness in A. contortrix of the same population used microsatellite markers to assign parentage of fathers (known mothers). Unlike our study, they found that snout‐vent length was positively correlated with reproductive success and that males were experiencing greater sexual selection. This relationship has been detected under natural conditions in other species of snakes. Although behavioural data are important in any mating system analysis, they should not stand alone to infer parentage, relationships or selection metrics (e.g. Bateman gradients). Long‐term sperm storage by females, female cryptic choice, and other factors contribute to the complexity of mating success of males. Accordingly, we thus conclude that estimates of reproductive success and fitness in cryptic species, such as copperheads and other snakes, require robust molecular methods to draw accurate conclusions regarding proximate and evolutionary responses. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 185–194.     

Characterization of beta-keratins in lizard epidermis: electrophoresis, immunocytochemical and in situ-hybridization study

Lizard scales are composed of alpha-(cyto-) keratins and beta-keratins. The characterization of the molecular weight and isoelectric point (pI) of alpha- and beta-keratins of lizard epidermis (Podarcis sicula) has been done by using two-dimensional electrophoresis, immunoblotting, and immunocytochemistry. Antibodies against cytokeratins, against a chicken scale beta-keratin or against lizard beta-keratin bands of 15-16 kDa, have been used to recognize alpha- and beta-keratins. Acid and basic cytokeratins of 42-67 kDa show a pI from 5.0 to 8.9. This indicates the presence of specific keratins for the formation of the stratum corneum. Main protein spots of beta-keratin at 15-17 kDa, and pI at 8.5, 8.2, and 6.7, and one spot at 10 kDa and pI at 7.3 were recognized. Therefore, beta-keratins are mainly basic proteins, and are used for the formation of the hard corneous layer of the epidermis. Ultrastructural immunocytochemistry confirms that beta-keratin is packed into large and dense bundles of beta-keratin cells of lizard epidermis. The use of a probe against a lizard beta-keratin in situ-hybridization studies confirms that the mRNA for beta-keratins is present in beta-cells and is localized around or even associated with beta-keratin filaments.     

An enigmatic marine reptile,Hispaniasaurus cranioelongatus (gen. et sp. nov.) with nothosauroid affinities from the Ladinian of the Iberian Range (Spain)

An incomplete skull of a marine reptile with an atypical elongation of the postorbital region is described. The find comes from the Muschelkalk facies (Cañete Formation) of the Villora section (Iberian Range, Cuenca Province, Spain), characterised by a shallow marine (intertidal) environment and dated as Ladinian in age. The small skull has a rectangular shape, lacking, as preserved, upper temporal openings and a parietal foramen. The upper temporal openings might be secondarily closed. However, the absence of a parietal foramen and squamosals in the preserved part and the incompleteness of the pterygoids make a posteriorly postponed location of the upper temporal openings also conceivable. Teeth are all broken off but alveolar spaces indicate large and massive maxillary dentition. Micro-CT-data revealed a highly vascularised inner structure of the dorsal skull elements, which might indicate special feeding adaptations. Adding the new find to an existing phylogenetic analysis of Triassic marine reptiles reveals eosauropterygian, especially nothosauroid, affinities. However, morphological differences to nothosauroids justify the erection of a new genus and species for this enigmatic marine reptile. Its atypical morphology, without any extinct or modern analogue, fits well with the continuously increasing diversity of Triassic marine reptiles, exhibiting various specialised feeding strategies urn:lsid:zoobank.org:act:6D75AEC7-A5C5-4844-B71A-8215AB099134     

Molecular genetic diversification of the lizard complex <Emphasis Type="Italic">Darevskia raddei</Emphasis> (Sauria: Lacertidae): Early stages of speciation

To characterize the molecular genetic diversity of the genus Darevskia, several populations were examined by the inter-SINE-PCR method, reporting the number and sizes of the spacers between individual copies of SINE-like interspersed repeats. Examination of 17 D. raddei geographical populations and several reference species revealed unequal genetic differences, measured as Nei and Li’s genetic distances (D_NL), for different groups of samples. The highest homogeneity was observed for the apparently panmictic D. raddei nairensis population from the basin of the Hrazdan River: genetic differences within each of the five samples and between them were similarly low (less than 0.1). The difference between ten samples of D. raddei raddei from Armenia and Karabakh (0.2–0.3) was somewhat higher than the interindividual difference within each sample (0.1–0.2), indicating that the samples belonged to different populations. The assumption was supported by the phylogenetic tree topology and multidimensional scaling. The differences between samples from the morphological subspecies D. raddei raddei and D. raddei nairensis ranged 0.3–0.4. The difference of two D. raddei raddei samples of Talysh (Azerbaijan) from other samples of the same subspecies corresponded to the subspecific level. The genetic distances between the good species D. raddei and D. rudis was 0.6–0.7. In terms of D_NL, a questionable population from northwestern Turkey (“D. tristis”) was closer to D. rudis (D_NL = 0.45), probably representing its subspecies. The phylogeography of D. raddei is discussed.