Circatidal swimming behaviors of fiddler crab Uca pugilator larvae from different tidal regimes

Abstract

Fiddler crab Uca pugilator larvae are released within estuaries near the time of high tide and are exported offshore to undergo development. Previous studies indicate that zoea-1 larvae use selective tidal-stream transport (STST) to migrate from adult habitats to shelf waters. In areas with semidiurnal tides, this behavior is mediated by a circatidal rhythm that is characterized by upward swimming toward the surface during ebb tide, followed by a descent toward the bottom during flood tide. We tested the hypothesis that U. pugilator zoeae from different tidal regimes possess activity rhythms that match local tidal patterns. Ovigerous crabs with late-stage embryos were collected from areas with semidiurnal, diurnal, and mixed tides and from an area within a microtidal coastal lagoon. Following hatching, swimming activity was monitored under constant conditions for 96 h. Zoeae from semidiurnal and diurnal regimes possessed activity rhythms with free-running periods that matched the tides at the collection sites (≈12.4 and 24.8 h, respectively). Crabs from beaches with mixed tides displayed asymmetrical oscillations in swimming activity with dominant periodicities that corresponded to the semidiurnal and diurnal constituents of the tides. Zoeae from microtidal areas possessed rhythms that were similar to those observed in crabs from areas with semidiurnal tides. At all locations, peaks in activity occurred during the time of expected ebb currents, which is consistent with STST behavior favoring seaward transport. Differences in larval activity patterns suggest that STST behaviors are controlled by separate circatidal and circalunidian clocks or paired circalunidian clocks coupled in antiphase.

Local tidal regime dictates plasticity of expression of locomotor activity rhythms of American horseshoe crabs, Limulus polyphemus

“…These tidal regimes vary throughout the North American range of L. polyphemus’ , along which at least four genetically distinct populations can be distinguished – Gulf of Maine (GM), Mid-Atlantic (MA), Atlantic Florida (AF), and Gulf of Florida (GF; King et al 2005, 2015) – each of which may experience very different tidal periodicities. Whereas the GM and MA populations experience two daily tides, the GF population experiences either one dominant daily tide (Rudloe 1980; Lopez-Duarte and Tankersley 2007), or strictly diurnal tides (one tide every 24.8 h). Furthermore, the AF population in the Indian River Lagoon inhabits a variable microtidal environment (Ehlinger and Tankersley 2009): northward of Melbourne, Florida, tides are very small (1–2 cm) and primarily weather driven, while two daily small (10–20 cm) tides may occur in the immediate vicinity of coastal inlets (Woodward-Clyde 1994).…”

“…Among some intertidal species that share a geographic distribution similar to that of L. polyphemus , individual populations express behavioral rhythms that match the periodicity of local tides (Stillman and Barnwell 2004; Lopez-Duarte and Tankersley 2007; Darnell et al 2010). For example, female blue crabs Callinectes sapidus from environments with two daily tides express circatidal rhythms consisting of two bouts of swimming activity per day, while those from environments with a single daily tide express unimodal circalunidian rhythms (activity approximately every 24.8 h, the length of a lunar day), and those from a non-tidal environment express circadian rhythms of activity (Darnell et al 2010).…”

“…Further, while adult fiddler crabs Uca princeps from regions with one dominant daily tide express both tidal and daily activity patterns, the magnitudes of the activity bouts match the amplitudes of the tides (Stillman and Barnwell 2004). Interestingly, while fiddler crab ( Uca pugilator ) larvae from the microtidal Indian River Lagoon express circatidal activity patterns in constant conditions after hatching in the laboratory (Lopez-Duarte and Tankersly 2007), green crab ( Carcinus maenas ) larvae from other microtidal regions are arrhythmic (Queiroga et al 2002). Across these species, differences in the rhythms expressed are hypothesized to be due to both intraspecific genetic variation and the influence of the environment during development (Queiroga et al 2002; Stillman and Barnwell 2004; Lopez-Duarte and Tankersly 2007).…”

Phenotypic plasticity in larval swimming behavior in estuarine and coastal crab populations

“…While we cannot conclusively determine whether the observed differences in larval behaviors in our study resulted from differences in genotypes or phenotypes without conducting reciprocal transplant experiments, we hypothesize that there were phenotypic differences created either by the abiotic conditions experienced by the developing embryos, such as salinity, or by differences in maternal behaviors, such as abdomen flapping (Barnwell, 1968;Lopez-Duarte and Tankersley, 2007a;Morgan, 1996). If the swimming behaviors were instead the result of differences between two genetically isolated populations, it would require that larvae hatched in each location spend six months together in a common offshore nursery area and then return to settle near their natal site, or else exhibit behaviors that are unsuitable to their new habitat (Barnwell, 1976;Thurman, 2004).…”

“…While estuarine crab larvae frequently exhibit complex swimming behaviors that aid their departure from estuaries, species from the outer coast may have simpler behaviors (Lopez-Duarte and Tankersley, 2007a;Lopez-Duarte et al, 2011;Miller and Morgan, 2013). No study, however, has compared larval swimming behaviors between different populations of the same species from estuarine and outer coast habitats to determine whether the behaviors are phenotypically plastic.…”