We examined colour pattern variation and female preference in 12 Trinidadian guppy populations spanning high- and low-predation streams. Male ornamentation was significantly more elaborate in low-predation sites, consistent with relaxed natural selection allowing sexual selection to drive phenotypic divergence. Female preference tests confirmed stronger discrimination for carotenoid-based orange spots in low-predation populations, supporting the sensory drive hypothesis.

Hybrid crosses between Xiphophorus hellerii and X. maculatus were used to investigate the genetic basis of melanoma development in the Xiphophorus melanoma model. F1 hybrids showed markedly elevated melanoma incidence compared to parental lines, with tumor development correlating with overexpression of the Xmrk oncogene. Reproductive performance metrics were comparable between hybrid and parental crosses under controlled laboratory conditions.

Guppy populations established in thermally elevated Mediterranean streams were characterized using microsatellite markers to reconstruct invasion history and assess genetic diversity. Stable isotope analysis revealed significant trophic overlap with native Luciobarbus populations. Electrofishing surveys over three years showed negative correlations between guppy density and native fish recruitment, suggesting competitive exclusion at high guppy densities.

This review synthesizes current understanding of the evolution of viviparity across the family Poeciliidae, covering placental structures, embryo nutrition strategies and the continuum from lecithotrophy to matrotrophy. Comparative genomic data from 38 poeciliid species are integrated with reproductive ecology observations to reconstruct the evolutionary trajectory of viviparity, identifying convergent and parallel evolutionary pathways.