Spatial variation in genomic signatures of local adaptation during the cane toad invasion of Australia

Adaptive evolution can facilitate species' range expansions across environmentally heterogeneous landscapes. However, serial founder effects can limit the efficacy of selection, and the evolution of increased dispersal during range expansions may result in gene flow swamping local adaptation. Here, we study how genetic drift, gene flow and selection interact during the cane toad's (Rhinella marina) invasion across the heterogeneous landscape of Australia. Following its introduction in 1935, the cane toad colonised eastern Australia and established several stable range edges. The ongoing, more rapid range expansion in north-central Australia has occurred concomitant with an evolved increase in dispersal capacity. Using reduced representation genomic data of Australian cane toads from the expansion front and from two areas of their established range, we test the hypothesis that high gene flow constrains local adaptation at the expansion front relative to established areas. Genetic analyses indicate the three study areas are genetically distinct but show similar levels of allelic richness, heterozygosity and inbreeding. Markedly higher gene flow or recency of colonisation at the expansion front have likely hindered local adaptation at the time of sampling, as indicated by reduced slopes of genetic-environment associations (GEAs) estimated using a novel application of geographically weighted regression that accounts for allele surfing; GEA slopes are significantly steeper in established parts of the range. Our work bolsters evidence supporting adaptation of invasive species post-introduction and adds novel evidence for differing strengths of evolutionary forces among geographic areas with different invasion histories.

The effect of pH on embryonal and larval development of the Caucasian Brown Frog, <i>Rana macrocnemis</i>

Aim. To study the effect of different pH values on the characteristics of the embryonic and larval development of Rana macrocnemis.

Material and methods. Fragments from 6–7 clutches of R. macrocnemis collected on the territory of Foothill Dagestan were used in the work. The experiment  included  two  series  of  experiments:  in  the  1st  series,  the entire cycle of embryonic‐larval development of the R. macrocnemis frog was  studied,  and  in  the  2nd,  only  the  postembryonic  development  of R. macrocnemis was studied. Eggs were individually placed in containers with different pH values (4.0, 5.0, and 9.0).

Results.    The    most    vulnerable    periods    in    the    development    of R. macrocnemis are the stages of neurula, limb formation, and metamorphosis. At pH 4.0, oxygen consumption by larvae decreases, accompanied by suppression of feeding behavior and a decrease in the intensity of metabolic processes. In addition, pH 4.0 has a negative effect on the survival of embryos and larvae. At pH 5.0, changes are noted that are mainly of an adaptive nature. Against the background of the accelerated development of embryos at these pH values, a significant decrease  in  the  length  and  weight  of  their  body  is  noted.  With  the transition to larval development, an increase in body size is observed against the background of a small increase in weight. An elongation of the duration of the period from the beginning of the formation of limbs to the end of metamorphosis was also noted.

Conclusion. The data obtained can be used in monitoring the level of acidity of the environment and the oxygen content in natural water bodies during the spawning period, which will help clarify the issue of the reduction in the number of R. macrocnemis frogs in Dagestan.

Direct and Latent Effects of Pathogen Exposure Across Native and Invasive Amphibian Life Stages

Emerging infectious diseases are one of the multiple factors contributing to the current "biodiversity crisis". As part of the worldwide biodiversity crisis, amphibian populations are declining globally. Chytridiomycosis, an emerging infectious disease, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is a major cause of amphibian population declines. This fungus primarily affects keratinized structures in larval, juvenile, and adult amphibians as well as heart function. However, we know little about how Bd can impact embryos as well as potential latent effects of Bd exposure over ontogeny. Using two different Bd strains and multiple exposure times, we examined the effects of Bd exposure in Pacific chorus frog (Pseudacris regilla), Western toad (Anaxyrus boreas) and American bullfrog (Lithobates catesbeianus) life stages. Using a factorial experimental design, embryos of these three species were exposed to Bd at early and late embryonic stages, with some individuals re-exposed after hatching. Embryonic Bd exposure resulted in differential survival as a function of host species, Bd strain and timing of exposure. P. regilla experienced embryonic mortality when exposed during later developmental stages to one Bd strain. There were no differences across the treatments in embryonic mortality of A. boreas and embryonic mortality of L. catesbeianus occurred in all Bd exposure treatments. We detected latent effects in A. boreas and L. catesbeianus larvae, as mortality increased when individuals had been exposed to any of the Bd strains during the embryonic stage. We also detected direct effects on larval mortality in all three anuran species as a function of Bd strain, and when individuals were double exposed (late in the embryonic stage and again as larvae). Our results suggest that exposure to Bd can directly affect embryo survival and has direct and latent effects on larvae survival of both native and invasive species. However, these impacts were highly context dependent, with timing of exposure and Bd strain influencing the severity of the effects.