Temporal window of receptivity and intraspecific variability in the responsiveness to metamorphosis-stimulating cues in the megalopa of a semi-terrestrial crab,Sesarma curacaoense

Abstract

SummaryThe larvae of numerous sessile and several motile marine invertebrate species respond to metamorphosis-stimulating cues, usually chemical signals from their benthic habitat. In three series of experiments (I-III), the megalopa larvae of a semi-terrestrial mangrove crab, Sesarma curacaoense de Man, were exposed for differential periods to adult-conditioned water (ACW), which had previously been found an effective cue. In the first experimental series (Exp. I), ACW was added on successively later days of the moulting cycle, while Exp. II comprised treatments in which the cues were provided from the first day (postmoult) and removed on sucessively later days. In Exp. III, the megalopae were exposed to ACW for 3 days at the beginning, in the middle, or near the end of the moulting cycle (days 1-3, 4-6, and 7-9, respectively). All experimental series also comprised a permanently exposed control group (C+) and another one kept in complete absence of the cue (C!), and all experiments were repeated with larvae originating from three different females (F1-F3 in Exps. I and II; F4-F6 in Exp. III). Both the timing and duration of exposure to ACW had a significant influence on the duration of development to metamorphosis, indicating an interaction between the extrinsic signal and the intrinsic (hormonal) control of the moulting cycle. While continuously exposed control megalopae (C+) required on average 7.6 ± 0.5 to 7.7 ± 0.5 d, those in group C! delayed their development by about 3-4 d (or on average by 48%), 7-9 d (119%), and 5-6 d (61%), respectively (F1-F3), indicating a great deal of intraspecific variability among hatches. In Exp. I, the cue had to have been added within about the first 6-7 d to become effective (no significant difference in development time between treatments and control C+), while a later addition of ACW had no more stimulating effect (no difference to C!). In Exp. II, metamorphosis was delayed in all treatments when the cue was removed after an initial exposure of less than 4-5 d, while later removal did not significantly reduce the stimulating effect of ACW. Together, the results from these two experimental series suggest that an exposure approximately during days 4-6 of the moulting cycle may be crucial as a temporal window of receptivity for the cue; this period coincides with the transition between intermoult and premoult (stages C-D 0 of Drach's classification system). Its presumable importance as a critical point was confirmed in Exp. III where development time was consistently shortest in megalopae exposed only during days 4-6 of the moulting cycle (no significant difference to control C+), while an earlier or later exposure prolonged development to metamorphosis. Intraspecific variability in the responsiveness to P. Gebauer et al. / IRD 47 (2005) 39-50 ACW was tested by comparing development time in control groups (C+, C!) among megalopae from 14 different hatches (including F1-F6). These data showed a significant variability both in the delay due to complete absence of the cue and ...

Effects of substratum and conspecific adults on the development and metamorphosis of Acanthocyclus hassleri (Brachyura: Bellidae) megalopae under laboratory conditions

“…If in this period, the larva could not find the adequate stimulus, a spontaneous metamorphosis occurred. This phenomenon has also been observed in other brachyuran species but with windows of receptivity of greater duration (Gebauer et al 1998(Gebauer et al , 2002(Gebauer et al , 2004(Gebauer et al , 2005. Previous experiences with larval development in A. hassleri indicates that the optimal development of the megalopa occurs at 17ºC (Barría et al 2005), higher than the temperature used in this experiment (12ºC).…”

Metamorphosis of a sesarmid river crab, Armases roberti : stimulation by adult odours versus inhibition by salinity stress

“…Significant differences between larvae produced by different females and reared under similar conditions have been observed in most larval features including survival, duration of development, biomass, growth rate, and in some species even in the number of larval stages (for references, see Anger 2001, Giménez andAnger 2003). Likewise, the extent of the metamorphosis-accelerating response to adult odours has been shown to reveal significant intraspecific variability (Gebauer et al 2005). This indicates that comparisons between results from different studies conducted with larvae from different conspecific females must be made with caution.…”

Recruitment limitation and competent settlement of sesarmid crab larvae within East African mangrove forests

“…Potential recruits use chemical cues from the parental habitat and/or conspecifics that are important in triggering larval moult cycles, development and eventually settlement (Gebauer et al 1998, 2002, O'Connor 2007, Simith & Diele 2008. Some species can independently shift through these life-history events following a genetic and hormonal program, while others rely heavily on environmental and chemical signalling (Gebauer et al 2005). Late-stage zoeae of brachyurans can rely on stimuli that alter their behaviour so that they position themselves within the water column to take advantage of transportation by depth-dependent currents (Christy & Morgan 1998, Kingsford et al 2002, Queiroga & Blanton 2005, Anger 2006.…”