Population biology and reproductive asynchrony of the pea crab Austinixa aidae and its host Callichirus corruptus in Northeastern Brazil

This study investigated the population dynamics of the symbiotic pea crab Austinixa aidae and its non-obligate host, the ghost shrimp Callichirus corruptus , on a sandy beach in Northeast Brazil, assessing the influence of the symbiotic relationship and environmental conditions on population traits. Monthly collections were conducted over 1 year at Cinelândia Beach, Aracaju, Sergipe, and specimens of both sexes were sexed and measured from individual burrows. We analysed size–frequency distributions, sex ratios, and reproductive periods, correlating them with each other and with environmental factors. A. aidae showed continuous seasonal reproduction, with peaks between June and August and in April, positively influenced by precipitation (the rainy season). Conversely, the host, C. corruptus , exhibited seasonal reproduction, peaking in February, which was correlated with higher temperatures (the dry season). This antagonistic reproductive pattern between the symbiont and host was confirmed by a significant negative correlation between their respective percentages of ovigerous females. Furthermore, a significant positive correlation was found between the number and size of crabs and the size of their host. Both species displayed smaller sizes than populations at higher latitudes, suggesting a latitudinal influence. This reproductive asynchrony may represent a coevolved strategy for the symbiont to avoid competition for resources during the host’s reproductive peak.