While our lab usually works on disease vectors, the questions that interest us draw us into many interesting side projects. In one such case, Dr. Gen Morinaga and John worked with Santa Clara University's Janice Edgerly to explore potential explanations for parental care in the insect order Embioptera, or webspinners (image shown below, courtesy of UBC). Our results, titled "Macroecology and Potential Drivers of Diversity in Webspinner Maternal Care (Order Embioptera)", are reported in Insect Systematics and Diversity (https://academic.oup.com/isd/article-abstract/7/1/1/6976708). Other than the YouTube link and the specimen below, all figures are from Morinaga et al. 2023, with a full citation at the end of this blog.
Dr. Edgerly studies webspinners for a range of reasons, including their interesting abilities to produce silk and their maternal care behaviors. They're also rather silly little animals - but don't take my word for it, take a look at a video Dr. Edgerly consulted on for public brodcasting:
For our study, Dr. Edgerly characterized their parental care behavior from dozens of species around the world. These species differ in how much silk they place over their eggs, the arrangement of silk and eggs, and the usage of other materials to cover eggs. There is considerable variation in how different species treat their eggs - but why?
One hypothesis relates to predation. If egg coverings help to protect eggs from predators, then they should be more common where predators are. On the other hand, it is also possible that instead, parental care evolved without predation pressure - perhaps in response to something else - and persisted in lineages simply due to the fact it already exists. In fact, these are not competing hypotheses - both could be true.
Measuring predation is hard, though. The primary predator for most Embioptera are ants. While knowing precisely where ants are the biggest threat is very difficult, we know that at a global level across groups of animals, annual evapotranspiration (AET) correlates very well with predation encounters. So, based on where Embioptera were found, we retrieved AET for those locations.
With a proxy of predation in hand, AET, we could see how it correlated with egg care behaviors, given the evolutionary history of the taxa in question. It is important to consider evolutionary history here, as species could exhibit parental care either due to the selection on their ancestors of that species (that is, evolving in response to predation) or because it was a trait inherited from some more distant ancestor and unrelated to predation pressures.
Next, we made aa composite variable that represented maternal care effort using a multiple correspondence analysis, a form of multivariate statistic that allows us to summarize categorical variables (like how eggs were being cared for by their mother)
We found statistical association between higher levels of maternal care and predation threat when accounting for evolutionary relationships, but it wasn't a perfect relationship. In fact, when non-native species were included in the analysis (named in the figure above), the association was much weaker (red points) than when only species sampled in their native ranges were used in the analysis (gray points). Now, all of these species exhibited quite high levels of maternal care, and evolution is often a gradual process, so they have not yet adapted to these new places. Were we able to sample these species in their native ranges, perhaps we would have had an even stronger association - or not.
Regardless, it appears that predation drives at least some maternal care in webspinners. Cool!
Morinaga, G., Soghigian, J., & Edgerly, J. S. (2023). Macroecology and Potential Drivers of Diversity in Webspinner Maternal Care (Order Embioptera). Insect Systematics and Diversity, 7(1), 1.
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