Geographic Variation in Size at Maturity in Brachyuran Crabs
Geographic variation in size of sexually mature females was compared in five species of crabs at sites spanning about 10 degrees of latitude along the east and west coasts of North America. Populations were sampled along the west coast at six sites for Pachygrapsus crassipes, four sites for Hernigrapsus nudus, eight sites for H. orgenensis, and two sites for Scyra acutifrons, and along the east coast at eight sites for Panopeus herbstii. Four of the five species showed significant geographic variation in size at onset of maturity, mean size, and size frequency distribution. P. herbstii and P. crassipes exhibited latitudinal variations and marked changes in population structure of mature females at biogeographic boundaries; P. herbstii matured at larger sizes at latitudes below Cape Hatteras; while P. crassipes matured at smaller sizes below Point Conception. H. nudus showed variation in the size distribution of mature females, but little variation in size at onset of maturity. For H. oregonensis and S. acutifrons, size at maturity varied on a local scale among neighboring populations. For S. acutifrons, a difference of about seven molts before the terminal molt at puberty was deduced to produce the observed variation in maturity. Its molt increment percentage was constant across all sizes of crabs and did not differ between two populations with disparate size structures. For H. oregonensis variation in molt increment and in the number of molts appears to account for differences in size at maturity among populations. Variation in maturation within H. oregonensis populations occurs over one to two molts, and a difference of about two molts accounts for differences in size at onset of maturity among populations. Geographic variations in growth and size structure of mature females in these species are likely to have major consequences for population fecundity and demography.
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Document Type: Research Article
Publication date: 1989-09-01
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