No abstract

Sex differences in body size and head dimensions are widespread in adult snakes, but because data are scarce for neonates, it is unclear whether differences are present from birth or arise post-natally. Here we analyse patterns of sexual dimorphism in neonates and adults of four species of natricine snakes, Nerodia sipedon, Storeria dekayi, Thamnophis radix, and T. sirtalis. Two measures of body size (snout±vent length, mass), four measures of head morphology (head length, head width, jaw length, and interocular distance), and tail length were obtained from wild-caught adults and from offspring born to wild-caught females. Among neonates, signi®cant sexual dimorphism was found in body size for S. dekayi and T. sirtalis, in head dimensions for S. dekayi, T. radix, and T. sirtalis, and in tail length for all four species. Among adults, signi®cant sexual dimorphism was found in body size, head dimensions, and tail length for all four species. The degree of sexual dimorphism in body size among adults greatly exceeded that among neonates. In contrast, the degree of sexual dimorphism in head dimensions was similar between neonates and adults. The presence of signi®cant sexual dimorphism among neonates suggests that hypotheses regarding the evolutionary signi®cance of sexual dimorphism in snakes should consider newborns as well as adults.

Within populations, the stochastic effect of genetic drift and deterministic effect of natural selection are potentially weakened or altered by gene flow among populations. The influence of gene flow on Lake Erie populations of the common garter snake has been of particular interest because of a discontinuous colour pattern polymorphism (striped vs. melanistic) that is a target of natural selection. We reassessed the relative contributions of gene flow and genetic drift using genetic data and population size estimates. We compared all combinations of two marker systems and two analytical approaches to the estimation of gene flow rates: allozymes (data previously published), microsatellite DNA (new data), the island model (FST‐based approach), and a coalescence‐based approach. For the coalescence approach, mutation rates and sampling effects were also investigated. While the two markers produced similar results, gene flow based on FST was considerably higher (Nm > 4) than that from the coalescence‐based method (Nm < 1). Estimates of gene flow are likely to be inflated by lack of migration‐drift equilibrium and changing population size. Potentially low rates of gene flow (Nm < 1), small population size at some sites, and positive correlations of number of microsatellite DNA alleles and island size and between M, mean ratio of number of alleles to range in allele size, and island size suggest that in addition to selection, random genetic drift may influence colour pattern frequencies. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 389–399.

We collected data on mortality of late-instar gypsy moth, Lymantria dispar (L.), from outbreak populations over 4 wk in June 2017 at 10 sites in the New England region of the United States, along with estimated rainfall at these sites. Deposition of airborne conidia of the fungal pathogen, Entomophaga maimaiga Humber, Shimazu & R.S. Soper, was measured at these same sites as well as at seven other locations in New England. We also quantified the geographical distribution of gypsy moth-caused defoliation in New England in 2017 and 2018 from Landsat imagery. Weekly mortality of gypsy moth larvae caused by E. maimaiga correlated with local deposition of conidia from the previous week, but not with rainfall. Mortality from this pathogen reached a peak during the last 2 wk of gypsy moth larval development and always exceeded that caused by LdNPV, the viral pathogen of gypsy moth that has long been associated with gypsy moth outbreaks, especially prior to 1989. Cotesia melanoscela (Ratzeburg) was by far the most abundant parasitoid recovered and caused an average of 12.6% cumulative parasitism, but varied widely among sites. Deposition of E. maimaiga conidia was highly correlated with percent land area defoliated by gypsy moths within distances of 1 and 2 km but was not significantly correlated with defoliation at distances greater than 2 km. This is the first study to relate deposition of airborne conidia of E. maimaiga to mortality of gypsy moths from that agent.

Hosts and their associated microbes are being increasingly introduced around the world, which can lead to novel host/microbe associations via new sympatries. Woodwasps (Hymenoptera: Siricidae) are able to utilize wood for its nutrients due to obligate mutualistic associations with white rot fungi in the genus Amylostereum and when invasive woodwasps are introduced to new areas, their symbionts accompany them. There is increasing evidence that woodwasp-fungus associations previously believed to be highly specific are actually flexible. We show that in North America, both Urocerus albicornis and Urocerus cressoni, which develop in trees in the Pinaceae, usually use Amylostereum chailletii but sometimes carry an Amylostereum areolatum strain putatively introduced to North America by the invasive woodwasp Sirex noctilio. Symbiont spillover from invasive to native hosts is a source of new host/introduced symbiont associations that could result in changes in microbes and host fitness with the potential to impact communities.