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Drought leads to reproductive quiescence in smooth-billed anis: Phenotypic evidence for opportunistic breeding and reproductive readiness
Authors:Mychel Raony Paiva Teixeira Morais  Tiago da Silva Teófilo  Bruna K G Azevedo  Diogo Manuel Lopes Paiva Cavalcanti  José Domingues Fontenele-Neto
Institution:1. Department of Biosciences, Biological and Health Sciences Center, Federal Rural University of the Semi-Arid Region, Mossoró, Rio Grande do Norte, Brazil

Department of Cell and Development Biology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, São Paulo, Brazil;2. Department of Biosciences, Biological and Health Sciences Center, Federal Rural University of the Semi-Arid Region, Mossoró, Rio Grande do Norte, Brazil

Abstract:Previous studies have suggested that the smooth-billed ani (Crotophaga ani, Linnaeus, 1758) breeds opportunistically following unpredictable rainfall in drought areas. To obtain proof of this phenomenon, the present study described and compared reproductive morphology and cell proliferation in the gonads of free-living smooth-billed anis during a wet season (April to June 2012) and the following dry season (July to September 2012) in a semiarid area using light and electron microscopy (transmission and scanning) and the AgNOR method. The morphological findings indicated distinct levels of reproductive activity related to seasonal changes. Morphological and morphometric analyses of the gonads confirmed intense gametogenic activity during the wet season, whereas gonadal involution occurred after rainfall ceased. The sizes of the testes and ovaries were significantly reduced compared to those in the wet season. The volumetric fraction of the seminiferous tubules in the testis decreased considerably, and no preovulatory follicles were detected in the ovary in the dry season. Moreover, the AgNOR count in the gonads revealed a significant decline in cell recruitment for gametogenesis after rainfall ceased. The histological findings indicated partial gonadal activation throughout the dry season. The analysis of the seminiferous epithelium confirmed the early testicular recrudescence phase, and sporadic postovulatory follicles indicated random ovulation during this time. The excurrent ducts and the oviduct also underwent remarkable involution in the dry season. Taken together, these findings confirm opportunistic breeding by smooth-billed anis in a semiarid habitat and suggest that gonadal recrudescence has been established as a reproductive strategy to cope with unexpected precipitation events.
Keywords:bird reproduction  cuculidae  histology  seasonal variation
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