Wednesday, June 9, 2010

Mediated design in diphyletic nectarivorous phyllostomids?

One of the cool things about being a scientist is using big words. Am I right? Sure I am.

Bats of the family Phyllostomidae are the most diverse of all the bat families. Phyllostomid bats include your standard bug-eating species (insectivores), but other species eat fruit (frugivores), nectar (nectarivores), and even blood (sanguivores - the vampire bats). That's a lot of variety for a single family. The nectarivores are interesting because they have a very specialized anatomy that supports their food of choice. They have small teeth and elongated snouts and tongues. They can also hover as they feed. It's easy to imagine that these attributes arising in an ancestral bat and then being passed along to its descendants. That would make them monophyletic.

According to a new paper in BMC Evolutionary Biology, that easily imagined scenario is probably not correct. In their article "Evolution of nectarivory in phyllostomid bats (Phyllostomidae Gray, 1825, Chiroptera: Mammalia)," Datzmann et al. report the results of their phylogenetic analysis of phyllostomids that showed that the nectarivorous bats are not monophyletic. Instead,
Our study provides strong support for diphyly of nectarivorous phyllostomids. This is remarkable, since their morphological adaptations to nutrition ... closely resemble each other. However, more precise examinations of their tongues (e.g. type and structure of papillae and muscular innervation) revealed levels of difference in line with an independent evolution of nectarivory in these bats.
See that part about "independent evolution" and "diphyly?" Datzmann et al. believe that the ability to eat nectar (and all the anatomical specializations that go with it) originated twice independently. It's called convergent evolution when two different evolutionary lineages acquire a similar adaptation. Given the complexity of the adaptations for nectarivory, this is a pretty amazing convergence.

From a creationist perspective, I would accept that these phyllostomid bats really are related to a common ancestor. I suspect that the rank of family is roughly equivalent to a baramin, so that means that the different feeding strategies of these phyllostomid bats really did arise from a single ancestral population. (Please note that there has been only one attempt to do phyllostomid bat baraminology, and it showed only that phyllostomids belonged to a single kind but did not exclude other bats). Assuming that Datzmann et al.'s phylogenetic analysis is correct, I think the diphyly of nectarivory might be an example of what I call mediated design.

The idea behind mediated design is that God created organisms something like a Swiss army knife. Swiss army knives have all manner of tools and gadgets packed into them, and generally you use only one tool at a time. So too with critters. God didn't just create organisms perfect for one situation, but He planned ahead, as it were, and equipped them with other traits that might be useful in a fallen environment. At some time after creation, the descendants of the original phyllostomid bats began expressing traits and behaviors that allowed them to exploit new food sources. These weren't just randomly acquired, but pre-planned. God's design for the bats was not implemented immediately at creation but instead was mediated through the phylogenetic history of the bats. Since these nectarivorous traits were planned and designed ahead of time, it's really not surprising at all to find them "originating independently" in two bat lineages.

Datzmann et al. 2010. Evolution of nectarivory in phyllostomid bats (Phyllostomidae Gray, 1825, Chiroptera: Mammalia). BMC Evolutionary Biology 10:165.

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