Anolis cristatellus wileyae – Does this pair from St. Thomas need to worry about Cyrtosomum infections? Read on.
I wanted to write a few posts about parasites because hey – anoles have some really neat parasites! First up are the nematodes in the genus Cyrtosomum, which have been reported from several anoles and some other lizard taxa like Sceloporus and Cyclura. You might remember Cyrtosomum because C. penneri was the worm that AA-contributor Gerrut Norval and his colleagues used to infer that the Taiwanese population of A. sagrei originated from Florida and not Hawaii, something that wasn’t clear from sagrei molecular data (cool!).
Aside from pinworms (we’ll get to these another day), Cyrtosomum species are probably the most widespread nematode parasites in anoles. They’re really small (difficult to see without magnification), and occur in really large numbers in the lizards’ large intestines (many hosts have worm burdens of 100-200). Until recently, we knew very little about their life history – we knew that they could multiply within a single host individual via infective larvae, but we didn’t know how they moved between host individuals. Several authors (including Norval et al.) noted that Cyrtosomum species are only found in adult lizards, and suggested the possibility that these are sexually transmitted parasites.
Okay, let’s just take a moment… Worms, from sex. Yep.
Gabe Langford and his students tested this hypothesis in C. penneri, and elegantly demonstrated that these worms are indeed transmitted between hosts during sex. It’s a nice paper that I recommend both because it’s an interesting read (AA in the acknowledgements!) and also because the authors apply some techniques that are probably unfamiliar but possibly useful for some anologists. They dyed the nematodes various colors, then used them to infer copulation between host individuals – might be a cool way to contrast copulation with paternity!
Anyhow, this sexual transmission suggests that there’d be a strong correlation in the evolution between anoles and their Cyrtosomum parasites because anoles are having sex with individuals from their same population most of the time. You might be familiar with this notion – that the parasite phylogeny should mirror the host phylogeny. It’s one of the oldest ideas in parasitology, and was eventually elevated to Rule status (this one’s called Fahrenholz’s Rule). The thing is, it’s not as common as folks once thought, and is probably more an exception than rule. I was pretty excited when I heard about Gabe’s work because hey, here’s a possible example of Fahrenholz’s Rule, and one where parasite life history traits might affect parasite diversification!
I had in the freezer about 60 Cyrtosomum scelopori from anoles I had collected in the Dominican Republic, and I sequenced them at a 370-bp fragment of ITS (that’s that small, typically variable region between ribosomal genes in the nuclear genome, and is unfortunately all that’s available for taxa residing on forgotten parts of the tree of life!). I made a haplotype network and didn’t expect much resolution, but did expect any clusters to contain worms sharing the same host species… Well, that kinda happened (look at the haplotype network if you didn’t already). Not surprisingly, there wasn’t much resolution, and worms from A. cybotes (from which I had the most samples) were all over the place. There is some geographic association that isn’t shown in the figure, but not much. With the exception of A. brevirostris, the other worms from lesser-sampled host species each have haplotypes that are generally clustered together. Did you notice A. cristatellus yet? Yep, those samples are from the introduced population in La Romana in the Dominican Republic, and there are no extant Cyrtosomum species in the source population or in any on Puerto Rico anoles, which suggests that the introduced population somehow acquired a sexually transmitted parasite from another species. There are a few possible explanations for this, and an obvious one is interspecific copulation – something that apparently does happen – and these worms suggest it may occur more than we realize.
Next up is a thorny-headed worm!
Gabe Langford
Nice post Bryan! Although I’m a bit biased. I like the addition of the network…we should chat about this stuff soon. I think interspecific mating between some Anolis spp. is more common than one might expect. Just like the link at the end of your post, my students and I have seen wild male A. sagrei copulate with A. carolinensis on a few occasions over the past 2 years. Recently, after reading Sven Vogler’s comment in the “Hanky Panky” post on AA, we were able to convince a recently captured large male A. sagrei to copulate with a female Hemidactylus frenatus in a semi-natural enclosure inside a greenhouse. I know it’s in the lab, but it suggests some of these males may make mistakes on occasion; but, that is all the opportunity these worms need!
BFalk
Thanks Gabe! I can’t believe you got sagrei to copulate with a Hemidactylus (you “convinced” him to do it?!). But yeah, let’s chat soon – there might be some more stuff we could do with Cyrtosomum. Oh and I collected some Rhabdias from Anolis that I think you might want!
Kuti Ra
I once caught a young female A.lineatopus that had a large white worm in her cloaca.The worm came out when she started to urinate and I removed it. I should think
that would be very uncomfortable seeing as the worm was about as long as her longest toe and there were probably more in there.
Poor anole!
Yoel Stuart
This suggests that sanitizing cloacal thermometers between lizards when doing catch-and-release temperature sampling could be quite important.