Racial Differences Between North American and European Forms of Balanus Balanoides

Abstract

After transplantation and acclimatization of populations of the barnacle Balanus balanoides from the coast of New England to the Menai Straits, differences in breeding behaviour persisted over a period of from 4 to 18 months. The two populations are believed to belong to distinct physiological races.The New England populations fertilized 1½–3 weeks in advance of adjacent British populations.Embryonic development in the post-cleavage stages of the New England population proceeded in vitro at about twice the rate of the development of the British population, under identical conditions.The volume of the eggs of the New England population was 1.3–1.6 times as great as the volume of the eggs of the British specimens.Both populations, when growing in British waters, liberated their nauplii in March at a time which coincided with the beginning of the vernal plankton increase in the locality. The embryos of the American population had therefore remained in the mantle space for a much longer period than had those of the British specimens and for a longer period than that reported for New England populations in their native habitat.In B. balanoides the time of fertilization and rate of development may be genetically adapted in each general locality so that the embryos reach full term before the plankton increase is due. The actual time of liberation is then mediated by the hatching substance in response to prevailing food conditions.If the B. balanoides population of the Western Atlantic area as a whole belongs to a physiological race distinct from that of the Eastern Atlantic, and responding differently to temperature levels at the breeding season, there is no reason to expect any close correlation in respect of environmental conditions between the southern limits of the species in Europe and in America.