Geographic Variation in Egg Size among Populations of the Mummichog, Fundulus heteroclitus (Pisces: Fundulidae)

Size of Fundulus heteroclitus eggs exhibited a clinal variation along the United States east coast, as well as in Chesapeake and Delaware bays. The general pattern of egg size variation was concordant with the distribution of two previously recognized subspecies and was characterized by smaller eggs at northern coastal and upper bay locations (F. heteroclitus macrolepidotus) and larger eggs at southern coastal and lower bay locations (F. h. heteroclitus), with intermediate egg size where the two forms come together. Variation was also detected at the inter- and intra-population levels. Variation among F. h. macrolepidotus populations was represented by differences in egg size between northern coastal and upper bay populations. A generally greater intra-population variation at a southern F. h. heteroclitus location resulted from a positive relationship between female size and egg size, while no such relationship was detected at a northern F. h. macrolepidotus location. The larger eggs of a southern population were also found to be heavier (dry weight) and to contain higher lipid content than eggs from the northern population. The variation in egg size among F. heteroclitus populations may be related to the survival of eggs deposited at different elevations within the intertidal zone.