Geographical Variation inFundulus heteroclitus: Tests for Concordance Between Egg and Adult Morphologies

Abstract

Recent studies have shown distinct patterns of variation in the egg morphology (oil droplet number, diameter and density of chorionic filaments) of Fundulus heteroclitus along the east coast (including Chesapeake and Delaware bays). We tested the hypothesis that variation in adult morphology and in electromorphs is concordant with that of egg morphology over the same range by subjecting data for these character sets to the Mantel test. This analysis was based on data for three egg characters, nineteen adult morphological (meristic and morphometric) characters and five protein characters from locations along the Atlantic coast. If the geographical differences observed among locations reflect genetic differences between two forms that have established secondary contact after isolation, we would expect general concordance between the different character sets. We would expect little concordance between the sets if they are each affected by different selectional and/or developmental responses to environmental regimes. Our analyses indicate that patterns of variation among localities for meristic, egg, and genetic character sets are all concordant, and thus the observed differences among locations are likely the result of secondary intergradation between two previously isolated forms. These conclusions are supported by similar patterns of geographical variation in spawning site preference and body coloration. Thus, these results support our earlier suggestion that these morphs should be treated as separate taxa, with F. h. heteroclitus occurring along the east coast from New Jersey south to Florida including lower Chesapeake and Delaware bays and F. h. macrolepidotus distributed from Connecticut north to Newfoundland with disjunct populations in upper Chesapeake and Delaware bays. Intergrade zones occur where the two morphs come together along the east coast in northern New Jersey and on Long Island, as well as in Chesapeake and Delaware bays