Research published in the journal Proceedings of the Royal Society B suggests female butterflies can smell if a potential male mate has a high occurrence of inbreeding in his lineage. The study found mating success of male butterflies was lower if they were inbred.
A butterfly is an insect primarily seen during the day that belongs to the Lepidoptera order, which includes both butterflies and moths. Like other holometabolous insects, the butterfly’s life cycle consists of four parts: egg, larva, pupa, and adult.
Butterflies are identifiable by their brightly colored wings and conspicuous, fluttering flight. The earliest known butterfly fossils date to the mid-Eocene epoch, going back 40 to 50 million years ago.
Butterflies exhibit polymorphism, mimicry, and aposematism (antipredator adaptations) in their physiology.
Scientists were curious as to the mating parameters of butterflies and wanted to determine how mates were selected. They wanted to examine how exactly female butterflies know which males to avoid?
It was assessed that inbred male butterflies produced and secreted less sex pheromones, thus making them less appealing to the opposite sex. Male butterflies emit pheromones that convey information about their species and genotype.
Pheromone use among insects has been especially well documented by entomologists. Pheromones are secreted or excreted chemical hormones that trigger a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual and impact the behavior of the receiving individual.
Pheromones can be used as an alarm mechanism alerting others to danger and or unleashed in self-defense, lead an invisible trail to food as ants do, and entice members of the opposite sex for breeding purposes. Pheromones are used from basic unicellular prokaryotes to complex multicellular eukaryotes, including humans.
Some vertebrates and plants communicate by using pheromones. Certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants. These tannins make the plants less appetizing for herbivores.
In mammals, these chemical signals are detected primarily by the vomeronasal organ (VNO) or Jacobson’s organ, a chemosensory olfactory (smell) organ located at the base of the nasal septum. The VNO is present in most amphibians, reptiles, and non-primate mammals but is absent in birds. In the case of butterflies, pheromones are detected via their antennas.
If animals, including humans, breed with a genetic relative their offspring will be inbred and more likely to have chromosomal genomic disorders; birth defects. Because of these disorders inbred males are often weaker and less able to defend the nest or provide food for their youngsters.
To ensure offspring will have the more optimal chance of fitness and survival, females are expected to avoid mating with a weak inbred male. Often inbred mates can be sterile. Therefore, for reproductive purposes, especially for egg-laying butterflies, it is essential they select mates that can adequately fertilize them. Otherwise, no offspring are produced.
For the study, the researchers produced inbred butterflies by ensuring that sisters could only reproduce with their own brothers. The male inbred offspring were then tested for their flight performance (as an index of general condition) and the amount of sex pheromones they produced. The researchers found that the general condition of the inbred males was worse and that they also produced less sex pheromones then normal outbred males.
After establishing the condition of the inbred males, researchers tested to see whether the low mating success of inbred males could be restored. Scientists released males and females together into a large cage. The genitals of the males were marked with fluorescent dust with different colors, each identifying for inbred and outbred males. During mating, this dust was transferred to the female and later detected using UV light. The antennae of some of the females were painted over with nail polish to prevent them from discerning the amount of sex pheromone produced by males.
During the experiment, females with the treated antennae (inhibited sense of smell) demonstrated no particular preference and mated with both inbred and outbred males equally. In contrast, females with untreated antennae (able to detect pheromones) mated more often with normal outbred males. These results indicate that the lower production of sex pheromones by inbred males, and not the general health of the inbred butterflies, is the reason for the low mating success of inbred males.
[Image via Shutterstock]