Resumen de Reproductive timing and larval dispersal of intertidal crabs: the predator avoidance hypothesis
- español
Muchos cangrejos intermareales y de aguas poco profundas tienen ciclos reproductivos marcados y larva migratoria. Las hembras liberan sus larvas durante las mareas nocturnas más altas, cuyas amplitudes coinciden con ciclos lunares o semilunares. Las larvas recién eclosionadas se mueven rápidamente mar adentro durante la noche donde, semanas después, alcanzan el estado de megalopa. En este estado, las larvas utilizan las mareas nocturnas para acercarse a la costa y al interior de los estuarios para establecer su hábitat en estado adulto. Inicialmente se pensó que estos crustáceos liberan sus larvas en forma simultánea de modo que al momento de alcanzar el estado de megalopa serían capaces de utilizar las mayores amplitudes de marea para movilizarse a su hábitat en estado adulto. Esta idea ha sido refutada por la observación de que especies de zonas costeras abiertas presentan patrones reproductivos similares a aquellas de estuarios. Como hipótesis alternativa, se planteó que las larvas abandonan rápidamente los estuarios durante la noche para escapar de depredadores visuales como peces planctívoros, abundantes en aguas poco profundas. La hipótesis anti-depredador ha recibido apoyo considerable: especies con larvas visualmente crípticas, con espinas y mejor protegidas de los depredadores carecen de ciclos reproductivos marcados y migración larval. Los mecanismos que causan esta sincronía reproductiva han sido poco estudiados. Documento evidencia en cuanto a que las hembras del cangrejo violinista ajustarían el momento de la fertilización de sus huevos para evitar variaciones en la temperatura de incubación que producirían errores de sincronía. Sin embargo, cangrejos de costas frías como en Chile aparentemente no muestran ciclos bi-semanales o mensuales de liberación de sus larvas. Las consecuencias de ello para las larvas y los adultos requiere ser examinado
- English
Many intertidal and shallow water crabs have strong reproductive cycles and migratory larvae. Females release larvae near the time of high water of the larger amplitude nocturnal tides during the semilunar or lunar cycles. Newly hatched larvae move quickly at night toward and into the sea where, weeks later, they develop to megalopae that then ride nocturnal flood tides inshore and up estuaries to settle in adult habitats. It was first thought that crabs might time larval release so that larvae will become megalopae when they can ride the larger amplitude spring flood tides to adult habitats. This idea was rejected when it was found that were was no change in the timing of hatching during the breeding season by several estuarine species that would compensate for the decrease in the larval development period as the water temperature increased. In addition, megalopae moved up-stream at night but not on the largest spring flood tides. Attention shifted to the possible value to larvae of leaving the estuary quickly to avoid high temperatures, low salinities or stranding. This idea was not supported when it was found that species on open coasts exhibit the same reproductive patterns as do estuarine species. Alternatively, by moving quickly to the ocean at night larvae may best escape visual planktivorous fishes that are especially abundant in shallow areas. This predator avoidance hypothesis has been broadly supported: species with larvae that are cryptic, spiny and better protected from predation lack both strong reproductive cycles and larval migration. The mechanisms that promote precise reproductive timing have been little studied. Evidence is presented that female fiddler crabs may adjust the timing of fertilization to compensate for variation in incubation temperatures that would otherwise induce timing errors. However, crabs on colder coasts, as in Chile, apparently do not exhibit biweekly or monthly cycles of larval release. The consequences of this for adults and larvae have yet to be explored
