Tests of reproductive isolation among species in the Fundulus notatus (Cyprinodontiformes: Fundulidae) species complex

Isolation and characterization of microsatellite loci for the blackstripe topminnow Fundulus notatus and their variability in two closely related species

A total of 17 polymorphic microsatellite loci were isolated from the blackstripe topminnow Fundulus notatus. In a sample of 29 individuals, these loci were found to possess two to 19 alleles with expected heterozygosity values ranging from 0.212 to 0.919 and all but one of the loci conformed to Hardy-Weinberg equilibrium expectations. Many of these loci were polymorphic in the closely related species Fundulus olivaceus and Fundulus euryzonus providing a set of markers that should prove useful in future ecological and evolutionary studies of members of this species complex.

Evolution of a sexually dimorphic trait in a broadly distributed topminnow (Fundulus olivaceus)

Understanding the interaction between sexual and natural selection within variable environments is crucial to our understanding of evolutionary processes. The handicap principle predicts females will prefer males with exaggerated traits provided those traits are indicators of male quality to ensure direct or indirect female benefits. Spatial variability in ecological factors is expected to alter the balance between sexual and natural selection that defines the evolution of such traits. Male and female blackspotted topminnows (Fundulidae: Fundulus olivaceus) display prominent black dorsolateral spots that are variable in number across its broad range. We investigated variability in spot phenotypes at 117 sites across 13 river systems and asked if the trait was sexually dimorphic and positively correlated with measures of fitness (condition and gonadosomatic index [GSI]). Laboratory and mesocosm experiments assessed female mate choice and predation pressure on spot phenotypes. Environmental and community data collected at sampling locations were used to assess predictive models of spot density at the individual, site, and river system level. Greater number of spots was positively correlated with measures of fitness in males. Males with more spots were preferred by females and suffered greater mortality due to predation. Water clarity (turbidity) was the best predictor of spot density on the drainage scale, indicating that sexual and natural selection for the trait may be mediated by local light environments.

Hatch success and temperature-dependent development time in two broadly distributed topminnows (Fundulidae)

Metabolic scaling laws predict a variety of emergent properties of biological systems based on relationships among temperature, body size, and rates of physiological processes. These models have been criticized as being overly simplistic and not accounting for directional variability arising from evolutionary tradeoffs. I measured hatch success and egg development time at six temperatures for 12 populations throughout the latitudinal range of two broadly distributed topminnows (Fundulus). I asked if hatch success and development time differed between the species and northern and southern populations. Hatch success reaction norms suggested that the more broadly (and northern) distributed Fundulus notatus was more eurythermic with a lower optima and broader performance breadth than Fundulus olivaceus. Temperature explained most variability in mass-corrected development time. Development time differed between the species, but not northern and southern populations. Deviations from predictions of universal scaling laws were most pronounced away from specie's thermal optima.