Ovarian cycles and microhabitat use in two species of topminnow, Fundulus olivaceus and F-euryzonus, from the southeastern United States

Differences in spawning seasonality, inferred from ovarian cycles, and microhabitat use for two closely related Fundulus species were not effective as potential reproductive isolating mechanisms. Seasonal spawning periodicity of F. olivaceus and F. euryzonus as shown by changes in mean egg diameter and mean number of mature eggs recovered from ovaries showed nearly identical temporal patterns in reproductive activity. Peak egg development was between April and May and was lowest by the end of August. Univariate comparisons of 11 environmental variables associated with aggregations of Fundulus spp. revealed highly significant differences in several of these variables. However, individuals of both species were frequently collected together, and microhabitat differences did not remove the potential for mismating.