ALBERT

Notes: Summary Mating preferences of individual females and mating patterns among marked crabs were studied during the summers of 1973–1976 on sand beaches in mangrove habitat on the west coast of Florida in order to determine if females choose mates indirectly on the basis of the quality of a resource males defend and females use during breeding, directly on the basis of male size, or both. Twice each lunar month for periods of 6–8 days when females are sexually receptive, mature males of all sizes fight for, court from and defend supratidal burrows in which females mate, oviposit and reside for about, 2 weeks while incubating their eggs. Large males win fights with small males, tend to court from burrows located higher on the beach than the burrows of small males and mate more often than small males. Males are sequentially polygynous and may mate with up to 3 females at a single burrow during each semilunar breeding period. Male and female sizes were positively correlated in 85 mated pairs because large females can not enter the burrows of small males. However, there were no significant differences among the sizes of the females who mated with males in 5 size classes (13.0–15.5 mm carapace length). Receptive females spent about 9.5 min sampling 1–12 males and burrows before choosing their mates. Most females began sampling soon after high tide, though some fed first in the lower intertidal zone. Individual females neither chose larger males or higher burrows among those they sampled nor did they move so as to encounter sequentially larger males or higher burrows. During periods with low tides, males of all sizes courted from burrows located at all positions on the elevation gradient and females chose neither significantly higher burrows nor significantly larger males. During periods with high tides, large males courted from, and females mated in high burrows. Choice of high burrows did not, however, result in choice of larger males considering either all those on the beach or only those at preferred up-beach locations. Most females mated in burrows that were high enough to escape structural collapse due to tidal inundation or flooding by a tidally driven rise in groundwater. The effects of burrow flooding and collapse on female breeding success may select for choice of stable burrows. Females probably choose stable burrows by assessing directly features of burrows themselves. Burrows appear to be a resource for females and their quality as breeding sites probably is determined largely by their structural integrity. Costs associated with the sampling behavior necessary for females to choose both a stable burrow and a large male may be sufficiently great to limit choice to burrow quality alone.