Guppy

Poecilia reticulata is a small (2–6 cm), sexually dimorphic livebearer of the family Poeciliidae, native to northeastern South America and Caribbean islands (Trinidad, Barbados, Venezuela, Guyana) but now introduced worldwide for mosquito control and the aquarium trade. Males are smaller (2–3.5 cm) and brilliantly colored with variable patterns of orange, blue, green, black, and iridescent spots, while females are larger (3–6 cm) and drab olive-gray. Males possess a modified anal fin (gonopodium) used for internal fertilization. Females are ovoviviparous, giving birth to live, free-swimming fry every 21–30 days, with brood sizes of 5–100+ depending on body size. The guppy is one of the most important model organisms in evolutionary biology, ecology, and behavioral genetics, famous for studies of sexual selection, predator-driven evolution, and color pattern genetics involving both autosomal and Y-linked genes. Wild populations in Trinidad have been used for landmark experimental evolution studies demonstrating rapid adaptation. They are highly adaptable, tolerant of variable water conditions (fresh to brackish), and omnivorous. In the aquarium hobby, centuries of selective breeding have produced hundreds of fancy strains with elaborate tail shapes and color patterns. The genome is fully sequenced and widely used in population genomics research.