The invitation for dinner sometimes comes with an unstated invitation for sex. In the Corynopoma riisei, the invitation is very explicit. Also known as swordtail characin, C. Riisei, is a freshwater fish native to Colombia, Trinidad and Tobago and Venezuela that is not uncommonly found in aquariums. They also have a very anthropogenic way to get laid.
When a male of this tropical freshwater species (Corynopoma riisei) wants to mate, he dangles an “ornament”—a flag-like appendage normally hidden close to his body—in front of his desired date. The ornaments come in different shapes and sizes, and researchers have suspected since the 1960s that the shapes reflect the females’ preferred foods. Now a team of researchers has confirmed this by studying female diet and male ornament variation in different populations of the fish. Ant-like ornaments (pictured) were a hit among the females who most heavily fed on ants that fell into the streams and rivers where the fish live; oval, egg-like ornaments were popular with females that preferred beetles and beetle larvae. The scientists were even able to reproduce the food-based attraction in the lab by introducing ants into the diets of aquarium-raised females who were fed flake food all their lives. After 10 days on the ant diet, these females preferred the ant-like ornaments to the beetle-like ones. The discovery, published online today in Current Biology, represents the first known example of males of any species evolving to look like dinner to better their chances with the opposite sex.
More information on the order Characiformes, which includes Tetras, piranhas, hatchetfishes, headstanders, and pencilfishes, can be found at the Tree of Life Project.
The order Characiformes includes a vast array of fishes that live in rivers and lakes of Africa and the New World (from Texas in North America through Central and South America). They are divided into 14 or 16 families, four of which are African (over 200 species), and the rest live mostly in the Neotropics (more than 1,200 species). They include well-known forms like piranhas, tetras (e.g. neon tetras, silver dollars), hatchetfishes, and pencilfishes, popular in the aquarium trade. Other characiforms also have commercial importance as a food resource for human communities living along the banks of broad tropical rivers. These include the African citharinids and the Neotropical prochilodontids, which are very abundant, large-bodied species, typically forming massive schools that migrate up and down the main river channels. Other characid groups (family Characidae) include important sport-fishing species, like the african tiger fish (genus Hydrocynus, subfamily Alestiinae), and the Neotropical dorados (genus Salminus, subfamily Bryconinae). These are voracious predators that may reach a size of 100-130 cm in length and a weight of up to 50 Kg. In contrast, the smallest characiform species, known as miniature forms (Weitzman and Vari, 1988), have adults that do not exceed 26 mm in length (some tetras, glandulocaudines, and lebiasinids).
None of the others invite a potential mate over for dinner first.