Reproductive output of Munida subrugosa (Decapoda: Anomura) from two localities of the Sub-Antarctic Magellan region: a latitudinal comparison.

TAPELLA, F.; VALIÑAS, M.S.; LOVRICH, G.; VINUESA, J.; ROMERO, M.C.

Ushuaia

Workshop; Interactions between the Magellan region and the Antartic/ Antartic benthic Deap- Sea Biodiversity.; 2003

The relation between the reproductive strategy and the latitudinal hábitat of invertebrates has been a widely subject of study. A shortened larval development and reduction in egg numbers with an increase in both larvae and egg-size with latitude was shown for several taxonomic groups, such as decapods, echinoderms and prosobranch mollusks. Differences in egg size likely reflect differences in maternal investment per embrio because a significant relationship between egg dimension and nutrient has been observed. Thus, reproductive patterns would serve as an ecological rule for adaptations at low temperatures and to seasonally pulsed food input at higher latitudes. However these adaptations were mainly shown in species taxonomically related, and the possible inter-specific variability was not considered as a bias factor. Therefore, the galateid crab Munida subrugosa, with a geographical distribution range of 20° of latitude, was selected to do a latitudinal comparison on fecundity, reproductive output, and size organic matter of eggs. During July 2001, samples of ovigerous female crabs were caught with an ephibenthic trawl in the Beagle Channel (54° 52´ S, 68° 15´ W) and Golfo San Jorge (47° 50´ S, 67° 50´ W). After sampling all crabs were immediately fixed in 6% buffered formaline seawater. In the laboratory, tha carapace length (CL) was measured with a digital calipter. Fecundity –as a number of eggs per brood- was determined, and the diameter of 15 eggs per female was measured. Egg clutches and individuals were dried at 55°C and combusted at 550° C. The organic matter of egg-clutches and crabs were calculated as the difference between ash and dry masses. The reproductive output (RO) was determined as the ratio between the organic matter of the brood and the female. Sine fecundity, egg diameter, and mass and organic matter of eggs may change during the embryonic development; ovigerous female were selected to have clutches at the same stage of development (eggs recently extruded, uniform yolk and no ocular pigment visible). Fecundity of M. subrugosa was positively correlated with crab size, and similar in both sampling location: the Beagle Channel and Golfo San Jorge (ANCOVA test; Pslope =0.115; Pordinate=0.928). However, eggs produced by M. subrugosa in the Beagle Channel were significantly larger (Student´s test; P 0.01) and with higher organic matter content than those produced in the Golfo San Jorge (Student´s test; P=0.014). Finally, the RO also correlated positively with crab size, and was higher in the Beagle Channel than in the Golfo San Jorge (ANCOVA test; Pslope =0.629; Pordinate 0.0019). Notwithstanding the similar fecundities of both populations of M. subrugosa, our results reinforce the hypothesis of increasing egg size and its organic matter towards high latitudes. Our results indicate that the reproductive investment of M. subrugosa increases with latitude because the RO was higher in the Beagle Channel. Consequently, we hypothesize that larval survival at high latitudes, where food availability is limited to short periods, should increase due to higher energetic contents of eggs.