Semilunar courtship rhythm of the fiddler crab Uca lactea in a habitat with great tidal variation

Abstract

Semilunar courtship rhythm is a widely distributed phenomenon among fiddler crabs in the genus Uca (Decapoda, Ocypodidae). Typically, synchronous courtship has been reported to peak near spring tides. To determine whether a region of large tidal variation shifts reproductive activity, we measured the frequency of specific courtship behaviors including claw-waving and semidome building for U. lactea males on Kanghwa Island, Korea. We found that synchronized courtship for U. lactea peaked near neap tides, whereas near the spring tides, seawater flooded the habitat and males predominantly fed on the mudflat. Although active females, which hold their burrows and usually feed on the mudflat, are abundant near to spring tides, males rarely claw-waved to attract females. This pattern is atypical for the species because other populations of U. lactea on Japan and Taiwan are synchronous around spring tides. We suggest that males invest most of their time in feeding during spring tides because foraging is limited during neap tides. During neap tides, males feed infrequently and thus expend stored energy on courtship signals. We conclude that patterns of reproductive synchrony may be dependent on food availability in periodically changing environments.

The effect of food availability on the semilunar courtship rhythm in the fiddler crab Uca lactea (de Haan) (Brachyura: Ocypodidae)

“…In a previous study, however, we found that their courtship rhythm was different from that of the same species in Japan (Kim 2002, Kim et al 2003. The courtship peaks did not occur at spring tides but nearer to neap tides.…”

Effect of food addition on the reproductive intensity and timing of both sexes of an intertidal crab

“…The habitat at the study site was not inundated by tides about half of each cycle and became dry. At this time these deposit feeders could not feed on organic material contained in the sediment (Kim et al 2004). The addition of food shifted the timing of male U. lactea reproductive activity earlier and increased the duration of activity (Kim & Choe 2003).…”

“…However, for lack of time, and because we found no differences between plots in the first experiment (see 'Results'), we did not observe the crabs for 4 d before we began to add food. During 3 d (30 March to 1 April) and 5 d (27 April to 1 May) between the 2 fortnightly cycles, we did not observe the crabs because the low tides were too early or late in the day for crabs to emerge, and the high tides were too low to fully cover the area with burrows, a condition that also suppresses crab surface activity (Kim et al 2004).…”

“…The timing of cycles of male courtship and female receptivity, which are nearly identical, may be determined by selection for the precise timing of larval release (Christy 2007) and may resist change due to variation in food availability or other environmental factors. However, studies of U. lactea in Korea found that food availability fluctuated with the semilunar cycle of tidal inundation and influenced both the timing and intensity of male courtship (Kim & Choe 2003, Kim et al 2004. This indicated a level of flexibility in reproductive investment by males that was not expected based only on selection for timing of larval release.…”

Food storage and carrion feeding in the fiddler crab Uca lactea

“…We also examined whether there were differences in storage behavior between sexes. Additionally, because feeding activity has been related to tidal rhythms in fiddler crabs (Kim et al 2004a), as well as in other animals (e.g. Meyer-Rochow & Brown 1998), storing frequencies were observed in relation to semilunar cycles and reproductive rhythms.…”