“Indirect development” increases reproductive plasticity and contributes to the success of scyphozoan jellyfish in the oceans

Ecologists and evolutionary biologists have been looking for the key(s) to the success of scyphomedusae through their long evolutionary history in multiple habitats. Their ability to generate young medusae (ephyrae) via two distinct reproductive strategies, strobilation or direct development from planula into ephyra without a polyp stage, has been a potential explanation. In addition to these reproductive modes, here we provide evidence of a third ephyral production which has been rarely observed and often confused with direct development from planula into ephyra. Planulae of Aurelia relicta Scorrano et al. 2017 and Cotylorhiza tuberculata (Macri 1778) settled and formed fully-grown polyps which transformed into ephyrae within several days. In distinction to monodisk strobilation, the basal polyp of indirect development was merely a non-tentaculate stalk that dissolved shortly after detachment of the ephyra. We provide a fully detailed description of this variant that increases reproductive plasticity within scyphozoan life cycles and is different than either true direct development or the monodisk strobilation. Our observations of this pattern in co-occurrence with mono- and polydisk strobilation in Aurelia spp. suggest that this reproductive mode may be crucial for the survival of some scyphozoan populations within the frame of a bet-hedging strategy and contribute to their long evolutionary success throughout the varied conditions of past and future oceans.

Morpho-meristics, maturity stages, GSI and gonadal hormone plasticity of African catfish Clarias gariepinus (Burchell 1822) that invaded into the Ganga River, India

Background African catfish Clarias gariepinus introduced to India has gravitated into the Ganga River as an invasive species. Morphological plasticity and reproductive adaptation are considered and reported as important manifestation contributing to evolution and persistence of an invasive species in the novel environment facilitating its expansion and establishment. African catfish in the Ganga River although documented to exist, it is yet to investigate if it elicits adaptation responses through morphological and reproductive plasticity in the riverine conditions. Therefore, morpho-meristic changes, plasticity in the reproductive stages, gonadosomatic index (GSI) and gonadal hormones were examined in C. gariepinus that invaded into the Ganga River so as to ascertain its invasion success. Results Out of 23 morpho-meristic characters examined, head length (HL), head depth (HD), anal fin length (AFL) and the pectoral fin rays (PECFR) were observed to differ significantly (p<0.05). The correlation coefficient ‘r’ between log length and log weight was found to be 0.9690 in culture and 0.8754 in river-caught specimens respectively. A distinct deviation in the maturity stages, GSI as well as gonadal hormones (testosterone, estradiol 17-β and vitellogenin) was further observed to change significantly in specimens of African catfish captured from the Ganga River as compared to those available in culture. Highest level of testosterone was found in males having gonadal stage V which was 184.82±10.4 pg/ml in culture and 204.82±21.34 pg/ml in river-captured specimens. The mean value of serum estradiol-17β was lowest (67.25±11.4 pg/ml) in gonadal maturity stage I and highest (328.73±24.5 pg/ml) in stage V in the river-captured C. gariepinus. The vitellogenin level in female C. gariepinus was detected in stage III, and it was maximum in stage V where it was 16.68±2.98 pg/ml in river-captured specimens and 12.63±2.12 pg/ml in cultured fish. Conclusion The results of this study on morpho-meristic and gonadal plasticity provide first evidence of invasion success of the African catfish gravitated in the Ganga River which has now adapted to the river environments for breeding and establishing. The variations concerning different reproductive phases and the gonadal hormones in culture and river-caught C. gariepinus have been considered to contribute to the success of the colonisation and establishment. The knowledge generated on the phenotypic and reproductive plasticity of African catfish available in the Ganga River will help management and control programmes.

Female fruitflies use gustatory cues to exhibit reproductive plasticity in response to the social environment

Animals can exhibit remarkable reproductive plasticity in response to their social surroundings, with profound fitness consequences. The study of such plasticity in females, particularly in same-sex interactions, has been severely neglected. Here we measured the impact of variation in the pre-mating social environment on reproductive success in females and tested the underlying mechanisms involved. We used the Drosophila melanogaster model system to test the effect of varying female group size prior to mating and deployed physical and genetic methods to manipulate the perception of different social cues and sensory pathways. We found that socially isolated females were significantly more likely to retain unfertilised eggs before mating, but to show the opposite pattern and lay significantly more fertilised eggs in the 24h after mating, in comparison to grouped females. More than 48h of exposure to other females was necessary for this socially-induced plasticity to be expressed. Neither olfactory nor visual cues were involved in mediating these responses. Instead, we found that females detected other females through direct contact with the deposits they leave behind, even in the absence of eggs. The results demonstrate that females show striking reproductive plasticity in response to their social surroundings and that the nature of their plastic reproductive responses, and the cues they use, differ markedly from those of males. The results emphasise the stark contrasts in how each sex realises reproductive success.