Dean Alan Croshaw

Excerpt: The Eastern Diamondback Rattlesnake, Crotalus adamanteus Palisot de Beauvois, 1799, is the largest rattlesnake species native to North America, reaching an average adult length of 130 cm (Conant & Collins 1991). The species is distributed throughout the southeastern United States, although populations are mostly located in Florida, Alabama, and southern Georgia. Despite a significant population decline since the 1950s (Timmerman & Martin 2003), mostly as a result of habitat loss, habitat fragmentation, and indiscriminate killings by humans (e.g., “rattlesnake roundups”, Means 2009), the species has not been afforded specific protection. Additionally, limited data are available on the most fundamental aspects of C. adamanteus biology, including population biology, life history, and population genetics (Hoss et al. 2010). As urbanization and other anthropogenic effects continue to degrade and destroy viable habitat, small and isolated biological preserves may be the last resort for this and similar species. However, snakes with large home ranges (such as C. adamanteus) may not benefit from small preserves because they are unlikely to meet the requirements for stable populations (Dodd et al. 1988, Timmerman 1995) and natural population genetic mechanisms may be compromised. For example, the population on our university campus, Florida Gulf Coast University (FGCU, Fort Myers, Florida, USA), may be rather small and isolated because of surrounding development. If so, inbreeding could lead to lowered heterozygosity and fitness.

Global population declines in herpetofauna have been documented extensively. Southern Florida, USA, is an especially vulnerable region because of high impacts from land development, associated hydrological alterations, and invasive exotic species. To ask whether certain snake species have decreased in abundance over recent decades, we performed a baseline road survey in 1993-1994 in a rural area of southwest Florida (Lee County) and repeated it 21 y later (2014-2015). We sampled a road survey route (17.5 km) for snakes by bicycle an average of 1.3 times a week (n = 45 surveys) from June 1993 through January 1994 and 1.7 times a week from June 2014 through January 2015 (n = 61 surveys). Snake mortality increased significantly after 21 y, but this result may be due to increased road traffic rather than expanding snake populations. The snake samples were highly dissimilar in the two periods, suggesting changes in species composition. For example, one species showed a highly significant decrease in abundance (Rough Greensnake, Opheodrys aestivus) while another showed substantial increases (Ring-necked Snake, Diadophis punctatus). Because of uncertain differences in traffic volume between 1993 and 2015, other species offered ambiguous results in their abundance trends. Nevertheless, four additional species contributed at least 12.1% dissimilarity (North American Racer, Coluber constrictor; Red Cornsnake, Pantherophis guttatus; Eastern Ribbonsnake, Thamnophis saurita; and Southern Watersnake, Nerodia fasciata). Increases in human land-use due to development and agriculture along with associated loss of wetlands and native habitats may have contributed to the changes we documented. Future work should seek to understand fully these causes and the conservation needs of declining species.

Moving beyond the basic concepts of autosomal Mendelian inheritance to sex-linkage can be difficult for introductory biology students. Although crosses with Drosophila fruit flies have long been a mainstay of genetics units that teach these concepts, they can be unwieldy for large numbers of students, take much of a semester to complete, and require substantial preparation time. We developed a guided exploration laboratory activity that illustrates the contrasts between sex-linked and autosomal inheritance mechanisms in one class period and can be applied easily in multiple sections of a large course. The activity sets up the background information of Thomas Hunt Morgan's famous crossing experiments that demonstrated sex linkage of the white eye color gene in Drosophila and asks students to apply skills learned in the previous autosomal inheritance unit to predict key aspects of his results (i.e., sex and phenotypic ratios of the F2 offspring). They then do a hands-on genetics laboratory activity by anesthetizing and sexing flies before analyzing provided data from Morgan's cross. Students interpret these results, pose an inheritance hypothesis, and revisit their original ratio predictions. Finally, review questions guide students toward recognizing and applying the contrasts between autosomal and sex-linked inheritance. We have tested this activity in over twenty of our own sections, assessed student performance with pre- and post-tests concerning sex-linked inheritance, and surveyed student opinion of the activity. Student response has been positive, both in terms of learning and enthusiasm. Our lesson can be modified and adapted easily to different classroom environments and course contexts.

Multiple mating by females is a widespread but often costly behavior. However, according to the Bateman principle, mating with multiple males may not increase the number of offspring produced by females. Despite the Bateman paradigm, many studies have shown advantages to polyandry. We investigated the fitness consequences of different mating regimes (virginity, once-mated, serial monogamy, and polyandry) in Drosophila arizonae, a species in which females remate frequently, experience a possible cost of mating in the form of an insemination reaction, and receive nutritive seminal contributions from males. Although monogamous and polyandrous females mated at similar rates, polyandry caused females to produce significantly more offspring for a longer period of their lives. Females with greater access to males laid significantly more eggs than those mated just once, and polyandrous females had a longer oviposition period than once mated females. Polyandrous females lived significantly longer than both virgin and serially monogamous females, suggesting that costs of mating are either low or offset by other benefits. A statistically significant interaction between the number of matings and mating treatment showed that additional matings allowed fitness increases for polyandrous, but not serially monogamous, flies. A direct fitness benefit for females by sperm replenishment is the most likely explanation for these results. Males may have partitioned their sperm and/or seminal fluid protein contributions to provide less for females they previously mated (i.e., the Coolidge effect), but male ejaculate exploitation and female effects are also possible. The high benefits and low costs of polyandry in our study contrast with other Drosophila papers and therefore highlight the extreme mating system diversity across the genus.Significance statementIn most mating systems, it is unclear why females mate with more than one male. Fruit fly females generally are expected to experience severe costs of mating. We used a highly promiscuous fruit fly species to test for costs and benefits to females of remaining virgins, mating once, remating many times with the same male (monogamy), and remating several times with a different male (polyandry). Polyandry was advantageous for females over monogamy because it allowed them to produce more adult offspring for a longer period of their lives. Additional copulations resulted in strong fitness increases for polyandrous, but not monogamous, female flies. Both polyandry and monogamy were better than mating just once because they allowed increases in egg and offspring production. Polyandry also conferred increases in lifespan over both virginity and monogamy. Therefore, we show benefits to mating with multiple males and failed to observe substantial costs of mating. The most likely explanation for our findings is a male effect by which they transfer fewer sperm and/or other ejaculate components to females they have previously mated (the Coolidge effect), though other mechanisms are possible.

Multiple paternity occurs in most species and animal groups that have been studied. Because mating involves fitness costs to individual females, theory predicts that polyandrous females gain greater fitness benefits than costs, allowing the behavior to be maintained. Genetic, rather than material, benefits often occur in species where males provide females with little more than sperm and seminal fluid. We compared fitness correlates of single- and double-sire clutches from female marbled salamanders (Ambystoma opacum) at the egg, hatchling, and metamorph stages of offspring development. Because clutches were collected from experimental breeding groups, strict paternity exclusion of offspring using microsatellite data allowed us to categorize each clutch as having either one or two fathers. Early offspring viability and size of hatchlings were not different between single-and multiple-paternity clutches. Larvae from the two clutch types were allowed to develop together in field enclosures until metamorphosis. Although there was no difference in size at metamorphosis, survival to metamorphosis was significantly higher in multiple-paternity clutches (44% vs. 40%) suggesting a benefit for females. The results were consistent with genetic benefits, although maternal effects could not be ruled out. The data did not support predictions of the genetic bet-hedging and good sperm hypotheses for genetic benefits of polyandry.

Understanding the phenotypic attributes that contribute to variance in mating and reproductive success is crucial in the study of evolution by sexual selection. In many animals, body size is an important trait because larger individuals enjoy greater fitness due to the ability to secure more mates and produce more offspring. Among males, this outcome is largely mediated by greater success in competition with rival males and (or) advantages in attractiveness to females. Here we tested the hypothesis that large male Marbled Salamanders (Ambystoma opacum (Gravenhorst, 1807)) mate with more females and produce more offspring than small males. In experimental breeding groups, we included males chosen specifically to represent a range of sizes. After gravid females mated and nested freely, we collected egg clutches and genotyped all adults and samples of hatchlings with highly variable microsatellite markers to assign paternity. Size had little effect on male mating and reproductive success. Breeding males were not bigger than nonbreeding males, mates of polyandrous females were not smaller than those of monogamous females, and there was no evidence for positive assortative mating by size. Although body size did not matter for male Marbled Salamanders, we documented considerable fitness variation and discuss alternative traits that could be undergoing sexual selection.

Herpetofaunal declines have been documented globally, and southern Florida, USA, is an especially vulnerable region because of high impacts from hydrological perturbations and nonindigenous species. To assess the extent of recent change in herpetofauna community composition, we established a baseline inventory during 1995-97 at a managed preserve in a habitat rich area of southwest Florida, and repeated our sampling methods fifteen years later (2010-11). Nine drift fence arrays were placed in four habitat types: mesic flatwood, mesic hammock, depression marsh, and wet prairie. Trapping occurred daily for one week during 7-8 sampling runs in each period (57 and 49 total sampling days, respectively). Species richness was maintained in mesic hammock habitats but varied in the others. Catch rates of several native species (Anaxyrus terrestris, Lithobates grylio, Anolis carolinensis, Nerodia fasciata) declined significantly. Other native species (Lithobates sphenocephalus, Siren lacertian, and Notophthalmus viridescens piaropicola) that were abundant in 1995-97 declined by greater than 50%. Catch rate of only two species (the nonindigenous Anolis sagrei and the native Diadophis punctatus) increased significantly. Hierarchical cluster analysis indicated similarity within habitat types but significant dissimilarity between sampling periods, confirming shifts in community composition. Analysis of individual species' contributions to overall similarity across habitats shows a shift from dominance of native species in the 1990s to increased importance of nonindigenous species in 2010-11. Although natural population fluctuations may have influenced differences between the two sampling periods, our results suggest considerable recent change in the structure and composition of this southwest Florida herpetofaunal community. The causes are unknown, but hydrological shifts and ecological impacts of nonindigenous species may have contributed.

Parasites and pathogens are noteworthy forces in evolutionary and population biology. Water molds are known to infect and kill amphibian eggs, and masses placed in clusters sometimes suffer greater losses. Thus, selection may favor single oviposition behavior in which females scatter individual eggs to avoid contact with dead eggs, thereby lowering the chances of hyphal spread. I tested the hypothesis that eggs in physical contact with dead eggs are more susceptible to death via pathogen infection using a singly laying urodele, the mole salamander, whose congeners mostly lay eggs in masses. Focal eggs were placed in replicated containers with variable egg contact (physically touching or separated) by treatment eggs that varied in status (dead or alive). The effect of egg arrangement was significant, with focal eggs surviving better to hatching when not contacting treatment eggs. Although treatment egg status (dead vs. alive) was not influential on its own, the interaction between egg contact and status was an important determinant of focal egg survival. Only when eggs were physically touching was it important whether they were dead or alive. Moreover, when eggs were touching there was a significant positive association between focal egg survival and the number of surviving treatment eggs. Water mold infected most dead eggs in all treatment groups. This study shows that mole salamander eggs are more likely to die when touching other eggs that have perished, most likely because of a greater chance of water mold infection. Such mortality may have contributed to diversification of egg-laying behavior in amphibians and shows a potentially compounding fitness cost of diminished fertilization success and embryo viability.

Terrestrial habitats surrounding isolated wetlands are a critical resource for many pond‐breeding amphibian species, yet few studies have examined the terrestrial distribution of post‐metamorphic juveniles and adults. We used an encircling drift fence at a breeding pond in conjunction with partial fences at 90, 172, and 332 m from the wetland to estimate the terrestrial distribution of adult marbled salamanders (Ambystoma opacum; four breeding seasons) and mole salamanders (A. talpoideum; two seasons), as well as the dispersion of newly metamorphosed A. opacum (one summer). For newly metamorphosed A. opacum, 79% emigrated <90 m from the wetland, and 8% moved beyond 172 m; movement distance was unrelated to body size. Distribution of adult A. opacum varied among years, with an average of 28% (range 23–31%) occurring beyond 172 m in all years. Averaged across two years, 51% of adult A. talpoideum occurred beyond 172 m. Lognormal models provided a good fit to both the juvenile and adult ambystomatid distributions, and parameters differed between age classes, sexes, species, and years within species. For adult A. opacum a buffer radius of 300 m or 340 m, depending on the year, is estimated to include 95% of adults; for A. talpoideum the estimate is 464 m or 501 m. A reanalysis of distribution data for seven ambystomatid species shows that a previous estimate of a 164‐m radius to protect 95% of a population underestimates the needed buffer radius by 185 m. Because our study wetland requires a nearly 500 m wide radius to protect 95% of its ambystomatid adults, preservation of similar communities may require much more surrounding terrestrial habitat than previously thought.