Showing papers by "Ryan L. Earley published in 2016"

The Genome of the Self-Fertilizing Mangrove Rivulus Fish, Kryptolebias marmoratus : A Model for Studying Phenotypic Plasticity and Adaptations to Extreme Environments

Abstract: The mangrove rivulus (Kryptolebias marmoratus) is one of two preferentially self-fertilizing hermaphroditic vertebrates. This mode of reproduction makes mangrove rivulus an important model for evolutionary and biomedical studies because long periods of self-fertilization result in naturally homozygous genotypes that can produce isogenic lineages without significant limitations associated with inbreeding depression. Over 400 isogenic lineages currently held in laboratories across the globe show considerable among-lineage variation in physiology, behavior, and life history traits that is maintained under common garden conditions. Temperature mediates the development of primary males and also sex change between hermaphrodites and secondary males, which makes the system ideal for the study of sex determination and sexual plasticity. Mangrove rivulus also exhibit remarkable adaptations to living in extreme environments, and the system has great promise to shed light on the evolution of terrestrial locomotion, aerial respiration, and broad tolerances to hypoxia, salinity, temperature, and environmental pollutants. Genome assembly of the mangrove rivulus allows the study of genes and gene families associated with the traits described above. Here we present a de novo assembled reference genome for the mangrove rivulus, with an approximately 900 Mb genome, including 27,328 annotated, predicted, protein-coding genes. Moreover, we are able to place more than 50% of the assembled genome onto a recently published linkage map. The genome provides an important addition to the linkage map and transcriptomic tools recently developed for this species that together provide critical resources for epigenetic, transcriptomic, and proteomic analyses. Moreover, the genome will serve as the foundation for addressing key questions in behavior, physiology, toxicology, and evolutionary biology.

Seeing orange: breeding convict cichlids exhibit heightened aggression against more colorful intruders

Abstract: Female convict cichlids (Amatitlania siquia) exhibit bright orange ventral coloration that males lack. The behavioral implications of this color are poorly understood, particularly in naturally occurring populations where female coloration could play a role in the expression of territorial nest-guarding behaviors. In this field experiment, monogamous breeding pairs of convict cichlids were presented with 3D printed model conspecific intruders of three body sizes (small, medium, and large) exhibiting three orange patch sizes (large, small, or none) to observe how territorial aggression varied as a function of intruder size and female coloration. Individuals occupying breeding pairs that were defending hatched offspring were significantly more aggressive toward intruders with small and large amounts of orange than toward models lacking orange, indicating that color is an important context-dependent elicitor of aggression in this species. Males were significantly more aggressive toward the intruder than females, and male aggression was strongly influenced by their size relative to the intruder. When males were smaller than the intruder, they performed significantly more aggressive acts than when they were the same size or larger than the intruder; this trend persisted across three putative populations in Lake Xiloa, Nicaragua. A potential explanation for these findings is that the orange color functions as a signal of individual quality or breeding readiness and that breeding pairs increase aggression to repel intruders that pose the greatest threat to pair bond and nest maintenance. One or both sexes of many animal species possess brightly colored features that might communicate information about overall heath or reproductive status. In convict cichlid fish, males and females establish pair bonds and jointly defend their nest and offspring. Single females exhibit striking orange coloration that males and breeding females lack. Our field-based experiment provided evidence that more colorful females, which likely pose a threat to pair bond stability and nest maintenance, incite more aggression from breeding pairs than drab females. Our study suggests that color provides salient information about, perhaps, female quality or readiness to breed in natural populations, and adds to a growing body of research that seeks to understand the varied roles that colorful ornaments play in animal communication.

Phenotypic differences between the sexes in the sexually plastic mangrove rivulus fish (Kryptolebias marmoratus).

Abstract: To maximize reproductive success, many animal species have evolved functional sex change. Theory predicts that transitions between sexes should occur when the fitness payoff of the current sex is exceeded by the fitness payoff of the opposite sex. We examined phenotypic differences between the sexes in a sex-changing vertebrate, the mangrove rivulus fish (Kryptolebias marmoratus), to elucidate potential factors that might drive the 'decision' to switch sex. Rivulus populations consist of self-fertilizing hermaphrodites and males. Hermaphrodites transition into males under certain environmental conditions, affording us the opportunity to generate 40 hermaphrodite-male pairs where, within a pair, individuals possessed identical genotypes despite being different sexes. We quantified steroid hormone levels, behavior (aggression and risk taking), metabolism and morphology (organ masses). We found that hermaphrodites were more aggressive and risk averse, and had higher maximum metabolic rates and larger gonadosomatic indices. Males had higher steroid hormone levels and showed correlations among hormones that hermaphrodites lacked. Males also had greater total mass and somatic body mass and possessed considerable fat stores. Our findings suggest that there are major differences between the sexes in energy allocation, with hermaphrodites exhibiting elevated maximum metabolic rates, and showing evidence of favoring investments in reproductive tissues over somatic growth. Our study serves as the foundation for future research investigating how environmental challenges affect both physiology and reproductive investment and, ultimately, how these changes dictate the transition between sexes.

Changes in reproductive physiology of mangrove rivulus Kryptolebias marmoratus following exposure to environmentally relevant doses of ethinyl oestradiol.

Abstract: Kryptolebias marmoratus exposed to 4 ng l(-1) of ethinyl oestradiol (EE2) for 30 days experienced significant changes in endogenous 17β-oestradiol (E2) and 11-ketotestosterone (KT) and qualitative changes in gonad morphology. Both hermaphrodites and males showed a significant decrease in E2, whereas only males exhibited a significant decrease in KT. Exposure to EE2 resulted in a decrease in spermatid and spermatocyte density in males and an increase in the number of early stage oocytes in hermaphrodites.

The relationship between handling time and cortisol release rates changes as a function of brain parasite densities in California killifish Fundulus parvipinnis.

Abstract: This study validated a technique for non-invasive hormone measurements in California killifish Fundulus parvipinnis, and looked for associations between cortisol (a stress hormone) and 11-ketotestosterone (KT, an androgen) release rates and the density or intensity of the trematode parasites Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB) in wild-caught, naturally infected F. parvipinnis. In experiment 1, F. parvipinnis were exposed to an acute stressor by lowering water levels to dorsal-fin height and repeatedly handling the fish over the course of an hour. Neither parasite was found to influence cortisol release rates in response to this acute stressor. In experiment 2, different F. parvipinnis were exposed on four consecutive days to the procedure for collecting water-borne hormone levels and release rates of 11-KT and cortisol were quantified. This design examined whether F. parvipinnis perceived the water-borne collection procedure to be a stressor, while also exploring how parasites influenced hormone release rates under conditions less stressful than those in experiment 1. No association was found between RENB and hormone release rates, or between EUHA and 11-KT release rates. The interaction between EUHA density and handling time, however, was an important predictor of cortisol release rates. The relationship between handling time and cortisol release rates was negative for F. parvipinnis harbouring low or intermediate density infections, and became positive for fish harbouring high densities of EUHA.

Hormonal Responses to Noncontact Aggression in Convict Cichlid Fish

Abstract: This study explored whether convict cichlid fish mount a hormonal response to aggressive encounters where dominance status remains unresolved. Hormone samples were collected at two time points before an aggressive interaction to obtain confinement-induced and baseline measures, and at one time point following a contest across a clear partition (experimental) or exposure to an opaque partition with an opponent on the opposite side (control). There was no overall significant effect of treatment (control vs. experimental) on hormone release rates but there were trends for cortisol and testosterone (T). A priori linear contrasts showed that individuals that engaged in aggressive interactions had lower postfight cortisol and T release rates than controls, suggesting that aggression, in this context, might attenuate the synthesis of both hormones. Cortisol decreased significantly between initial confinement and baseline, indicating that individuals habituate to the water-borne hormone collection procedure. Contrary to expectation, individuals with higher baseline T and 11-ketotestosterone (KT) release rates took longer to initiate conflict. None of the other measures of behavior were predicted by baseline hormone release rates, and contest behavior did not predict postfight hormone release rates. There was a significant positive relationship between KT and T at all time points. As with studies that employ mirror image stimulation, we found no hormonal response to unresolved contests despite high levels of aggressive behavior. Our study is unique because we demonstrate that animals engaged in conflict with live opponents also do not mount a significant hormonal response when clear dominance relationships are not established.