Colette M. St. Mary

Agriculture Alters Gonadal Form and Function in the Toad Bufo marinus

Background Many agricultural contaminants disrupt endocrine systems of wildlife. However, evidence of endocrine disruption in wild amphibians living in agricultural areas has been controversial. Typically, studies on the effects of pollutants on wildlife attempt to compare polluted with unpolluted sites. Objectives We took a novel approach to address this question by explicitly quantifying the relationship between gonadal abnormalities and habitats characterized by differing degrees of agricultural activity. Methods We quantified the occurrence of gonadal abnormalities and measures of gonadal function in at least 20 giant toads (Bufo marinus) from each of five sites that occur along a gradient of increasing agricultural land use from 0 to 97%. Results The number of abnormalities and frequency of intersex gonads increased with agriculture in a dose-dependent fashion. These gonadal abnormalities were associated with altered gonadal function. Testosterone, but not 17β-estradiol, concentrations were altered and secondary sexual traits were either feminized (increased skin mottling) or demasculinized (reduced forearm width and nuptial pad number) in intersex toads. Based on the end points we examined, female morphology and physiology did not differ across sites. However, males from agricultural areas had hormone concentrations and secondary sexual traits that were intermediate between intersex toads and non-agricultural male toads. Skin coloration at the most agricultural site was not sexually dimorphic; males had female coloration. Conclusions Steroid hormone concentrations and secondary sexual traits correlate with reproductive activity and success, so affected toads likely have reduced reproductive success. These reproductive abnormalities could certainly contribute to amphibian population declines occurring in areas exposed to agricultural contaminants.

Sexual selection for male parental care in the sand goby, Pomatoschistus minutus

Male parental care is typically thought to come at a cost to mate attraction and future mating success. However, it has also been hypothesized that paternal care may be under sexual, as well as natural, selection, such that good fathers actually attract more mates. Here we show experimentally that in the sand goby, Pomatoschistus minutus, females prefer to mate with males that provide higher levels of parental care. We manipulated male behavior using (1) different nest sizes and (2) an application of low-O2 water in the nests, and found that females consistently preferred males with elevated levels of care in dichotomous mate choice tests. This complements our earlier study in which we showed that males increase the amount and quality of care they provide in the presence of females. Our results demonstrate that male care may have evolved as a result of sexual selection rather than natural selection alone, and furthermore, that male care may not necessarily be in conflict with mate attraction.

Sequential Patterns of Sex Allocation in Simultaneous Hermaphrodites: Do We Need Models That Specifically Incorporate This Complexity?

Theoretical and empirical studies of sex allocation usually treat sequential and simultaneous hermaphroditism as distinct and disparate forms of allocation. However, the sexual patterns of numerous species have both sequential (e.g., size‐based) and simultaneous components. In most cases, we have drawn from sex allocation theory developed for sequential hermaphrodites to explain ontogenetic changes in allocation and from theory developed for simultaneous hermaphrodites to explain the remaining aspects of these sexual patterns rather than develop a more integrated theory. Here I present the evolutionary stable solution (ESS) to a dynamic statevariable model that explicitly combines the effects of size and simultaneous allocation to male and female function in a dynamic game. The model structure and initial parameter values are based on the sexual pattern of the blue‐banded goby, Lythrypnus dalli, a simultaneous hermaphrodite. I then compare the natural patterns of sex allocation in L. dalli with the predictions of the model and with those of a dynamic version of the size advantage model. The integrated model predicted variation in allocation, sex‐specific size distributions, and seasonal sex ratio better than the sequential hermaphroditism model did. Indeed, the sequential model, using L. dalli parameter values, predicts a dioecious rather than sequentially hermaphroditic allocation pattern. The comparison of these two models illustrates the disadvantage of drawing from two bodies of theory without a formal integrated framework. Furthermore, the comparison focuses attention on the role of costs of reallocation in the evolution of mixed (or intermediate) sexual patterns.

Artificial Reefs, the Attraction-production Issue, and Density Dependence in Marine Ornamental Fishes

Artificial reefs may provide a useful tool to enhance production of marine ornamentals and to divert detrimental harvesting activities from sensitive natural habitat. The efficacy of this strategy depends, in part, on the extent to which artificial reefs contribute to new production (vs. attract fishes from natural habitat) and therefore benefit harvested populations on a local and regional basis. Here the attraction and production hypotheses and their application to marine ornamentals are presented. Specifically, it is discussed how the strength and timing of density dependence can affect the response of fish population dynamics to artificial reefs. In addition to this discussion, examples of density dependence in marine ornamentals and related reef fishes are provided. Based on this information, a simple conceptual model is presented to clarify the role of density dependence, and this is followed by a discussion on the use of artificial reefs in the management and production of marine ornamentals. Finally, unresolved scientific issues that remain to be addressed are provided.

Parental responses to changes in costs and benefits along an environmental gradient

We evaluated the effects of dissolved oxygen on offspring survival, parental costs, and the pattern of parental care in Florida flagfish, Jordanella floridae (Cyprinodontidae). Specifically, we quantified (1) embryonic development and survival in the absence of parental care, (2) behavior of non-reproductive adults, and (3) behavior of parental males across a gradient in dissolved oxygen. Embryo developmental rates and survivorship increased with dissolved oxygen, with a relatively sharp increase in survival between medium and high oxygen treatments. Non-reproductive adults increased their frequency of aquatic surface respiration, reduced overall activity, and increased opercular beat rate as oxygen declined, suggesting increased costs of activity with reduced oxygen. Taking these cost measures together, costs appear to increase slowly as oxygen starts to decline and then increase sharply as conditions approach hypoxia. In contrast, parental effort increased gradually with dissolved oxygen. We conclude that the increase in care from low to medium oxygen primarily results from a sharp decline in physiological costs, whereas the continued increase in care from medium to high oxygen primarily results from an increase in offspring value. In addition, our results highlight that the benefits of fanning for offspring are not well understood and that they may increase with oxygen, contrary to what has been previously assumed.

A Macroevolutionary Perspective on Multiple Sexual Traits in the Phasianidae (Galliformes)

Traits involved in sexual signaling are ubiquitous among animals. Although a single trait appears sufficient to convey information, many sexually dimorphic species exhibit multiple sexual signals, which may be costly to signalers and receivers. Given that one signal may be enough, there are many microevolutionary hypotheses to explain the evolution of multiple signals. Here we extend these hypotheses to a macroevolutionary scale and compare those predictions to the patterns of gains and losses of sexual dimorphism in pheasants and partridges. Among nine dimorphic characters, including six intersexual signals and three indicators of competitive ability, all exhibited both gains and losses of dimorphism within the group. Although theories of intersexual selection emphasize gain and elaboration, those six characters exhibited greater rates of loss than gain; in contrast, the competitive traits showed a slight bias towards gains. The available models, when examined in a macroevolutionary framework, did not yield unique predictions, making it difficult to distinguish among them. Even with this limitation, when the predictions of these alternative models were compared with the heterogeneous patterns of evolution of dimorphism in phasianids, it is clear that many different selective processes have been involved in the evolution of sexual signals in this group.

The net effects of guarding on egg survivorship in the flagfish, Jordanella floridae

We investigated the effects of male nest guarding on egg survival in the flagfish, a species in which paternal care is thought to be relatively recently evolved. Thus, we characterized the fitness consequences of a major component of paternal care when secondary adaptations to care are likely to be minimal. The effects of guarding under three predation regimes were examined by exposing eggs to treatments in which no predators, conspecific females, and conspecific females and the egg predator Gambusia affinis were present. These were crossed with the presence and absence of parental males. We expected that guarding would result in an increase in egg survival in the presence of egg predators, but considered that in their absence the benefit might be decreased or absent, as a result of filial cannibalism. We also examined effects on egg survivorship stemming from filial cannibalism and egg-directed components of care (i.e. cleaning and fanning); the effects of these behaviours were examined through treatments in which males had full access to eggs (i.e. complete care), males were separated from their eggs by a screen (i.e. egg fanning and no cannibalism), and males were absent (i.e. no care and no cannibalism). In accordance with our expectations, guarding increased egg survivorship in the presence of females and Gambusia. However, egg survivorship when males were alone with eggs was low. Indeed, significantly more eggs were eaten than became diseased, suggesting that males cannibalize healthy eggs. Neither fanning nor cleaning resulted in an increase in egg survivorship. Thus, in flagfish, there may be costs of care when predators are absent. We discuss our findings in relation to sexual selection and the early evolution of parental care.

Reproductive fitness consequences of filial cannibalism in the flagfish, Jordanella floridae

We investigated the effects of filial cannibalism, which is prevalent in teleosts that display parental care, on components of fitness in the flagfish. Currently, filial cannibalism in care-giving teleosts is thought to reflect an adaptive trade-off between current and future reproduction, in which energy or nutrients gained from consuming eggs is invested into future reproduction. Thus, we expected filial cannibalism to increase future reproductive success. We quantified the reproductive fitness consequences of filial cannibalism in the flagfish by comparing two cannibalism treatments (male access to eggs versus no male access to eggs) crossed with two feeding treatments (high and low food). Males were followed over 90 days, approximately one breeding season (i.e. the expected reproductive lifetime of flagfish), and we considered three fitness components: (1) the total number of eggs received (2) the number of spawnings and (3) the frequency of spawning. Contrary to predictions, filial cannibalism reduced male reproductive success. While there was an effect of food on components of fitness (i.e. number of eggs received, number of spawnings, frequency of spawning), there was no effect of filial cannibalism. An enhanced diet was also related to increased male weight, but filial cannibalism was not. Thus, in the flagfish, we have no evidence that energy or nutrients gained from filial cannibalism is directly translated into increased future reproductive success. We discuss our findings in relation to current and alternative theories of filial cannibalism.

EFFECTS OF BODY SIZE ON GROWTH, SURVIVORSHIP, AND REPRODUCTION IN THE BANDED CORAL SHRIMP, STENOPUS HISPIDUS

Abstract Herein, we detail several important life-history parameters of the banded coral shrimp, Stenopus hispidus, a popular marine ornamental shrimp. Among the life history parameters described are 1) size at settlement, 2) molt interval, 3) post-settlement mortality and movement, 4) growth, and 5) relative fecundity. Overall, we document the effects of body size on several life-history parameters. Molt interval increased and growth increments declined as shrimp body size increased. Furthermore, mortality was size-specific in S. hispidus; large individuals had higher survival rates than smaller individuals. We also show that variation in size at settlement of S. hispidus in the upper Florida Keys, U.S.A., was much smaller than that found in previous studies from other parts of the world. Based on field measures of size at settlement, molting probability, and growth increment per molt, we developed a crustacean growth model, which included discontinuous growth and natural variability in the parameters. With it, we describe expected patterns of growth and post-settlement age for S. hispidus in the upper Florida Keys. Finally, we document positive relationships among female body size, egg mass volume, and egg number.

Sex Allocation in Lythrypnus (Gobiidae): Variations on a Hermaphroditic Theme

The gonadal sexual patterns of three Atlantic/Caribbean Lythrypnus (L. nesiotes, L. phorellus, L. spilus) are described, based on histological examination, and compared with previously described sexual patterns of L. dalli and L. zebra, from the eastern Pacific. Overall, there was striking similarity in the sexual patterns of all the species; each exhibited simultaneous hermaphroditism with a high degree of variability in allocation to male tissue among individuals. Among the five species whose sexual patterns are described, at least three distinct sexual patterns were identified. Lythrypnus dalli has an allocation pattern distinct from the other species, with populations consisting of primarily pure females, strongly female-biased hermaphrodites and pure males. Lythrypnus nesiotes was also found to be distinct from the other species, consisting primarily of pure females and strongly female-biased hermaphrodites and male-biased individuals (mean allocation to male tissue = 75%). In contrast to L. dalli, L. nesiotes had no pure males. Indeed, no other species examined included pure males. L. phorellus, L. spilus and L. zebra had much more intermediate allocation patterns than either L. dalli or L. nesiotes. Most individuals were female biased (<10% male tissue), and there were significant numbers of individuals with intermediate allocation (10–90% male). L. zebra differed somewhat from L. phorellus and L. spilus in that more strongly male-biased individuals were common in the sample (i.e., ranging in allocation from 90 to 98% male); this difference was not statistically compelling. This marked variation in allocation among closely related species suggests Lythrypnus is a useful model system to explore factors affecting allocation. For example, models developed for simultaneous hermaphrodites and appropriate for Lythrypnus predict that pure sexed individuals will be more common at higher density (e.g., because mating success is more certain). The observed interspecific variation supports this prediction – both L. dalli and L. nesiotes occur at high density and have the most extreme allocation patterns, whereas L. phorellus, L. spilus, and L. zebra occur at lower density and have more intermediate allocation patterns.