Reproductive biology of Macrobrachium amazonicum (Heller, 1862) populations with distinct phenotypes in Neotropical reservoirs during the 'El Niño' event
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Here, we investigated the reproductive biology (frequency and distribution patterns of ovigerous females, fecundity, reproductive output and egg size and volume) of Macrobrachium amazonicum in four populations living in Neotropical reservoirs, so as to verify whether this process was affected by the 2014-2016 'El Niño' event. The following two phenotypes were identified: in two populations, small-size (SS) females (CL: 9.05 and 10.06 mm) carried few eggs (X: 141 and 219) with a larger volume (X: 0.188 and 0.212 mm 3 ), whereas, in the other two populations, large-size (LS) females (CL: 15.89 and 14.51 mm) carried many eggs (X: 814 and 846) with a smaller volume (X: 0.130 and 0.143 mm 3 ). All populations showed continuous reproduction and similar reproductive output. 'El Niño' did not directly affect both phenotypes, which is a reflection of the reproductive plasticity observed in this species. This phenomenon acted as a stressing factor, modifying the reproductive patterns of the species in a space-temporal scale. Ovigerous females showed specificity in habitat use, with SS females being associated with macrophytes in deeper environments (refuges), and LS females being associated with shallow sandy areas (shelter and nursery). The high variability of reproductive aspects is better explained by intrinsic factors and could be implying an incipient speciation.