Wednesday, October 14, 2015

Plants and insect diversity

Hexapoda, the insects and their relatives, includes over half of all described species. Because large proportions of this diversity cluster within a small set of phytophagous groups, dietary substrates have been proposed to shape patterns of richness within the clade through antagonistic coevolution and zones of ecological opportunity.

For a long time the richness of the insect has been regarded as linked with their plant-feeding habits especially when unusually species rich were compared with their nearest relatives. Researchers have often been intrigued by the fact there are some incredibly rich plant-feeding insect groups, while other groups are not so diverse. This might be also only half the truth as many large scale DNA Barcoding programs show that groups thought to be species-poor contain a large number of cryptic species waiting to be discovered and described. 

But even if we accept the discrepancies in diversity for some of those groups the relationship between insect diet and diversity might not be that simple. In a new analysis, based on the most complete tree of insect relationships to date, researchers at York University showed that plant and insect diversity is more loosely linked that previously believed.

We wanted to explore how species are distributed between different insect groups, because not all groups of insects are species rich. What kinds of groups are rich should tell you why they are. We found that there is not a consistent association between plant feeding and high species richness, which was a bit of a surprise. We coded all the different groups for what they feed on and then looked more closely at which diets are consistently associated with higher or lower richness.

It turns out that different diets evolved at different times in evolutionary history and are gained and lost at different rates. This might be a possible explanation as to why some dietary options are connected to very species rich groups. However, it seems that this is not caused by general differences in the rate at which they diversify.

More likely there is a complex relationship between diet and the rate of diversification. It might be that to become very species rich on a particular diet, you need to use a particular kind of niche, or you need a particular adaptation that other groups don't have. This more complex picture is going to take a lot of working out.

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