Raelynn Deaton

Female masculinization and reproductive life history in the western mosquitofish ( Gambusia affinis )

In this study, we explored the relationship between female masculinization and various morphological and reproductive parameters of male and female western mosquitofish (Gambusia affinis), including body size, anal fin length, testes mass and female fecundity. We detected high levels of female masculinization in the Brazos and Little Brazos Rivers (Falls County, Texas) in March 2008, but not 2009. In both populations, masculinized females were smaller, possessed shorter anal fins, and had significantly lower total fecundity (collective number of eggs and embryos) compared to non-masculinized females. In addition, 2008 non-masculinized females were smaller and less fecund than 2009 non-masculinized females in both populations. Moreover, 2008 males were smaller, had shorter gonopodia, and smaller testes than 2009 males. Our results support the hypothesis that female masculinization can have a strong influence on reproductive life history and population dynamics of livebearing fishes.

Molecular Analysis of Hybridization between the Box Turtles Terrapene carolina and T. ornata

Abstract Hybridization of the box turtles Terrapene carolina and T. ornata has been reported throughout their sympatric range. Herein, eight polymorphic microsatellite loci and one mitochondrial polymorphism were used to assess patterns of introgression between these two species, both of which are of conservation concern. We estimated standard population statistics, population assignments, and ancestry for 28 T. carolina, 17 T. ornata, and ten putative T. carolina–T. ornata hybrids from southwest Texas. Both parental populations had high observed heterozygosity and allelic diversity, and there was high gene flow between the two parental species. Ancestry values were sporadic and typical of species that have been hybridizing. Approximately 86% and 76% of T. carolina and T. ornata, respectively, were correctly assigned to their species. Seven of the hybrids had a high level of ancestry for T. carolina and three resembled T. ornata. Interestingly, all T. carolina, putative hybrids, and one T. ornata had haplotypes of T. carolina, whereas all but one T. ornata had haplotypes of T. ornata. These results suggest that hybridization has occurred for several generations within this population, and we discuss how such hybridization may influence population structure for such species of concern.

Short term changes in sex ratio and density alter coercive male mating tactics

Short term fluctuations in operational sex ratio (OSR) and density can strongly influence male mating, often exacerbating conflict between males and females. Livebearing fishes of the genus Gambusia are ideal for investigating sexual conflict because males of all sizes mate coercively. In this study, we tested how short-term fluctuations in OSR and density influence coercive male mating behaviours. Specifically, we tested the prediction that as OSR becomes more female biased, males will mate with all available females. In contrast, as OSR becomes more male biased, male aggression will inhibit mating frequency. As predicted, males mated with more females as the number of available females increased. Moreover, males were less aggressive as the proportion of females increased and more aggressive as the number of males increased. This resulted in an inverse relationship between mating and aggression with OSR and density. Coercive males attempt to maximize their reproductive success by mating with all available females, which supports classic theory on the impact of OSR and density on reproductive activity.

Isolation and characterization of polymorphic microsatellite loci for the three-toed box turtle (Terrapene carolina triunguis) and cross-amplification in other Terrapene species.

We isolated and characterized eight polymorphic microsatellite loci for a Texas population of three‐toed box turtle, Terrapene carolina triunguis, using a refined hybridization capture procedure. All eight primer pairs amplified successfully at all loci in seven Texas ornate box turtles (T. ornata ornata). Due to the decline and conservation concerns of North American box turtles, these isolated microsatellites may be a most valuable tool for evaluating baseline population genetic structure for threatened box turtle populations.

Effects of a trematode infestation on body condition, reproduction and mating behaviors in a livebearing fish

Most studies of parasite-mediated sexual selection target organisms where female or male mate choice is the major driving force of sexual selection, leaving the effects of parasites on coercive mating systems understudied. Here, we investigated the role of a trematode infestation (black spot disease (BSD)) on female body condition, female fecundity, male coercion, and female resistance in a coercive livebearing fish (the western mosquitofish, Gambusia affinis). We tested the following predictions: (1) infected females are in poorer body condition and have lower fecundity than uninfected females; (2) males prefer to coerce uninfected females; (3) infected males coerce less frequently than uninfected males; and (4) infected females are less resistant to male coercion. In contrast to our first prediction, infected females had more energy reserves than uninfected females during one month and infected females had increased fecundity compared to uninfected females. In the behavior experiments, we found BSD influenced male coercion in two of our experiments supporting our third, but not second or fourth, prediction. These results suggest this parasitic infestation may play a minor role in sexual selection on G. affinis.

RELATIVE SIZE OF MALES AND COMPETITION FOR FEMALES INDUCES HOMOSEXUAL BEHAVIOR IN THE WESTERN MOSQUITOFISH (GAMBUSIA AFFINIS) UNDER LABORATORY CONDITIONS

Abstract In an ongoing experiment, we investigated how mating behaviors of male western mosquitofish Gambusia affinis change across a range of temperatures. During behavioral trials, we observed high levels of homosexual behavior between males when in a competitive situation. We observed that when two males are in competition for matings with females, the smaller male performed significantly more homosexual acts than the larger. These results suggest that a dominance relationship develops with males in competition, where large males may dominate small males by not allowing them to copulate with the female, thereby causing an increase in same-sex mating by smaller males. Although preliminary data also indicate a possible relationship between density of males and number of homosexual copulations, we were not able to statistically analyze the relationship because these observations occurred during an ongoing experiment. In a future study, we will seek to understand underlying causes of homosexual behavior in the western mosquitofish.

Parasitic Nematodes Decrease Fecundity in the Western Mosquitofish, Gambusia affinis

Abstract I tested effects of infection by the parasitic larval nematode Eustrongylides ignotus on reproduction in the livebearing western mosquitofish Gambusia affinis. Generally, parasitized females had fewer developing broods than nonparasitized females. Parasitic nematodes significantly reduced fecundity in the western mosquitofish.

GONOPODIAL STRUCTURES REVISITED: VARIATION IN GENITAL MORPHOLOGY WITHIN AND ACROSS FOUR POPULATIONS OF THE WESTERN MOSQUITOFISH (GAMBUSIA AFFINIS) IN TEXAS

Abstract We report on gonopodial structures in the western mosquitofish (Gambusia affinis) including forked distal hooks and presence-absence of the elbow and gap. In addition, we present information on gonopodial variation across the Trinity, San Jacinto, and Brazos river drainages in Texas. Resumen Reportamos la estructuras gonopodiales en el pez-mosquito (Gambusia affinis) incluyendo las horquillas de los ganchos distales y presencia-ausencia del codo y brechas del gonopodio. Además, se presenta información sobre la variabilidad en el gonopodio a través de las cuencas de los ríos Trinity, San Jacinto, y Brazos en Texas.

Development and cross-amplification of nine novel Gambusia geiseri microsatellite loci in G. clark-hubbsi and the endangered G. nobilis

The largespring Gambusia, Gambusia geiseri, is a stenohaline livebearing fish (Poeciliidae) native to the headwaters of the San Marcos and Comal Rivers, Texas. After introductions for mosquito control (circa 1930), founder populations persisted in several cool water spring systems throughout west Texas, making them invasive and ideal for studies in evolutionary and conservation biology. Herein, we developed nine polymorphic microsatellite primers for G. geiseri, which also cross-amplified in the rare G. clark-hubbsi and endangered G. nobilis. Allelic diversities were 9.25, 6.00, and 3.00 in each of the respective species with only one locus being monomorphic in G. nobilis. Overall heterozygosity was high with an average observed heterozygosity of 0.624, 0.622, and 0.308 and one, three, and three loci deviated from Hardy–Weinberg equilibrium in G. geiseri, G. clark-hubbsi, and G. nobilis, respectively. These primers may prove useful in future behavioral and evolutionary studies of these and possibly other Gambusia species. Moreover, the successful cross-amplification of these primers will aid in assessing the status of other rare and endangered Gambusia species.