Maternal effects vary between source populations in the Atlantic tomcod Microgadus tomcod

Abstract

Identifying the sources of variation in traits of larvae is one of the first steps in interpreting the role of phenotypic variation in recruitment. We examined the contributions of geographic source and parentage to phenotypic variation in offspring traits in a gadid, Microgadus tomcod, from 2 contrasting yet nearby locations. Adults were collected from the Hudson River (HR), a polluted riverine estuary with strong freshwater and tidal fluxes, and Shinnecock Bay (SB), a relatively clean barrier beach and lagoon system with minimal freshwater inflows. Eggs were stripped from fish in the laboratory and incubated in a common environment. Female and offspring traits varied substantially between populations. Females from SB had a higher ovary weight and gonado-somatic index (GSI) relative to body length, and produced larger eggs. Contrary to expectation, higher female condition did not result in larvae of better condition. SB offspring had smaller yolk reserves at hatch and were less resistant to starvation than offspring from HR, though size at hatching did not differ between the 2 populations. SB offspring took 25% longer to hatch, thereby increasing dependence on yolk reserves as embryos. This may represent a trade-off in time to hatching versus quality at hatching in tomcod from different environments. Geographic source accounted for more variance than maternal effects in time to hatch (90%) and yolk volume at hatch (42%). Maternal influence accounted for more variance in egg diameter (90%), length at hatch (33%) and starvation resistance (30%), though none of these measures was correlated to female size or age. These results emphasize differences in early life history traits across a small geographic scale and the extent to which offspring differences due to maternal effects depend on the local environment.