Sexual selection alone could spark formation of new species

A new study by University of Pittsburgh researchers indicates animals that seek mates and fight rivals that resemble their parents could be behaving in ways that lead to the formation of new species.

A strawberry poison frog, colour morph blue, is photographed climbing a tree in the Aguacate region of Bocas Del Toro,
Panama. These types of frogs' unique colouration will either attract mates of the same colour or encourage fights between
males of the same colour, according to a study published by Yusan Yang, a graduate student in the Richards Zawacki
Lab in the Department of Biological Sciences, and associate professor and lab director Corrine Richards-Zawacki.
The findings indicate that, over time, the behaviour could lead to two different colour types
 becoming two different species [Credit: Richards-Zawacki Lab]

The study by Yusan Yang, a graduate student in the Richards-Zawacki Lab in the Department of Biological Sciences and associate professor Corinne Richards-Zawacki, examines behavioural imprinting--the phenomenon of offspring learning a parent's appearance to choose future mates or distinguish rivals--in the strawberry poison frog (Oophaga pumilio).

This central American frog has a wide variety of colour types. The mother frog raises their tadpoles by feeding them unfertilized eggs. This mother-offspring interaction, the team discovered, influences the behaviours of the offspring: females grow up to prefer mates that have the same colour as their mother and males grow up to be more aggressive when their rival has the same colour as their mother.

The team developed a mathematical model to demonstrate how these imprinted behaviours can contribute to the formation of new species. Because of the imprinted preferences, females mate more with similar coloured males, and less with differently coloured males, which, over time, could lead to two colour types becoming separate species.

"Sexual selection is traditionally thought of as a strong driving force for the formation of new species. But several theoretical models have suggested it was not incredibly likely to do so without natural selection or geographic separation," explained Yang.

"One of the reasons is because it is hard to maintain multiple mating types in the population. Usually, natural selection can serve the role, but our model suggests that imprinted male aggression can also do it. This means that with imprinting in both sexes, sexual selection on its own could potentially kick start speciation."

The study was focused on amphibians, but the results could shed light on the evolution of many other animal species with imprinting, and in general where new species come from.

"Speciation is a key process in biology that has led to the amazing diversity of species we see today. How that happens is a fundamental question in evolution and one we've been trying to answer since the time of Charles Darwin," said Richards-Zawacki.

The findings are published in Nature.

Source: University of Pittsburgh [October 17, 2019]