Eat fat or better? See how the female butterfly decides

Male, orange female and Alba female bean powder butterfly (from left to right).

As you wander through the garden, have you ever wondered why butterflies take on such a beautiful variety of colors? Recently, evolutionary biologists from Stockholm University in Sweden have discovered the location and key components of the orange-white transfer switch by analyzing orange and white individuals in Collias crocea, and the related paper was published in the journal Nature Communications.

In most bean powder butterflies, all males and most females are orange or yellow, but there are also some females that are white. This white female butterfly, known as Alba, is common in every generation, making up 5 to 30 percent of females. But because orange/yellow wings are an important signal for identifying mates, scientists speculate that alba female butterflies should be at a disadvantage. For nearly a century, scientists have been exploring why female Alba butterflies are produced and maintained in butterfly populations.

Previous studies in the bean flour butterfly have found that orange female butterflies will invest energy resources into synthetic pigments, while Alba female butterflies will redistribute these resources from pigment production to other developmental processes. It is speculated that as a result of this redistribution, Alba females have a higher fat content and fecundity compared to orange females. However, males prefer to mate with orange females, which should be the price Alba females pay for this. Although previous research work has identified many biological and abiotic factors that maintain color polymorphisms in the wild, the genetic basis of this is still unknown.

To understand the mechanism by which Alba female butterflies are produced, scientists at Stockholm University used different research methods. First, to identify the gene region that causes the albinism, the researchers sequenced the genome of Colias crocea, found a single gene region associated with color differences, and found in that region the transposon factor insertion unique to Alba female butterflies, the insertion site is near a gene called BarH-1, which previous studies found that BarH-1 plays an important role in the development of pigment particles in drosophila eyes. And compared to orange females, Alba females have far fewer pigment particles on their wings. Subsequently, the researchers used antibody staining to detect the presence of BarH-1 in the developing wings. The results found that in the early stages of pupa development, the BarH-1 protein was only present in the cells of the alba female wing scales, suggesting that BarH-1 may play a role in the orange-white color transition by inhibiting the formation of pigment particles.

To test this functional prediction, the researchers used CRISPR/Cas9 gene editing to produce a chimera that knocked out BarH-1. These chimeric females have white and orange chimeric wings. Further studies have found that orange scales have more pigment particles than white scales, similar to the wing scales of normal orange butterflies. These findings demonstrate that BarH-1 in wing scale-building cells produces whiteness by inhibiting the formation of pigment particles, but this function does not occur in males or orange females.

Previous studies have shown that the same mechanism causes ingestion in all butterfly species. To validate this prediction, the researchers examined whether the albino females of the North American species Colias eurytheme also contained fewer pigment particles, and found that this was indeed the case, suggesting that BarH-1 inhibits the formation of pigment particles beyond the cloud yellow butterfly. Additional studies have shown that Alba females have more abdominal fat reserves than orange females, which is consistent with previous studies of orange-white butterflies. These results suggest an interesting possibility that the cause of albinism may be the same for all bean flour butterflies, but this requires further research in more species.

Based on these findings, the research team believes that the bean meal butterfly reduces the formation of pigment particles through a simple Y-shaped redistribution model, resulting in reduced pigment synthesis, so that more resources can be freely used for other developmental processes, thus ensuring the proportion of Alba female butterflies in each generation. However, in other tissues or developmental periods, the physiological components associated with Alba may also be influenced by BarH-1 or other genes surrounding transposing factor insertion sites. In addition, other mutations near the insertion point may also cause these features. The researchers will next test these alternative hypotheses and determine whether the Alba phenotype has a single genetic basis in the genus Bean meal butterfly.

Editor: Hua Hua Reviewer: Seamus Editor:Zhang Meng

Journal Source: Nature Communications

Issue Number: 2041-1723

Original link: https://www.eurekalert.org/pub_releases/2019-12/su-gih121719.php

The content of the Chinese is for reference only, and all contents are subject to the original English version. Please indicate the source of the reprint.