Latitudinal variation in the reproductive biology of Betaeus truncatus (Decapoda: Alpheidae) along the Chilean coast

The extensive coast of Chile with its relatively homogeneous water masses favors a wide distribution of marine invertebrates, including the snapping shrimp Betaeus truncatus. We selected one sampling site in northern (Guanaqueros) and two sites in southern Chile (Metri and Putemün) to study latitudinal variation in the reproductive biology of B. truncatus. Monthly samples were collected over a one-year period (1994–95). The smallest ovigerous female was collected in northern Chile, but large-sized females with eggs were obtained principally in southern Chile. Females produced up to 1067 eggs per clutch (Guanaqueros), and average clutch size ranged from 234 (Putemún) to 399 eggs (Guanaqueros). The relationship between fecundity and female size differed significantly between Guanaqueros and the other two southern populations studied. Recently laid eggs in Metri and Putemún were significantly larger than those extruded in northern Chile, and egg volume increased during embryogenesis between 80.8% (Putem ú n) and 184.9% (Metri). Brood mortality was significantly higher in Metri (41.4%) compared to Guanaqueros (20.8%) and Putemün (19.1%). Eggs produced in northern Chile contained the highest percentage of water. Egg dry mass as well as reproductive output increased from north to south. We compare our data with those published for other decapod species, and discuss the observed latitudinal clines.