The parasite in question. Photo from an Anole Annals post by Gerrut Norval.
Recently, Bryan Falk wrote an interesting report on how nematode parasites are passed from one anole to another by sexual contact. He summarized a fascinating paper by Langford et al. in the Journal of Parasitology that convincingly demonstrated this phenomenon. In reading that paper, I found one idea they suggested in the Discussion to be particularly intriguing. I’ll let them describe it:
“Our finding that C. penneri” (the nematode parasite) “is transmitted by copulation has some interesting implications for the host’s reproductive and behavioral biology. Anolis sagrei reproduces in a female-defense polygyny, wherein large males (e.g., SVL = 50 mm) establish and maintain territories containing multiple, relatively small females (Schoener and Schoener, 1980). In Anolis mating systems, young males are generally thought to have little mating success because they are excluded from females by large territorial males (Losos, 2009). In contrast, our parasitological results suggest that small male lizards are copulating with mature females and becoming infected with a sexually transmitted parasite. Thus, our results provide some support for the female mimicry hypothesis (Orrell and Jenssen, 2003) and/or the ‘‘dear enemy’’ phenomenon (Paterson, 2002) in anoles. This insight into A. sagrei reproduction should encourage anologists to reconsider the role of covert and satellite males in anole mating systems where C. penneri infects small male lizards. In conclusion, the major contribution of our study is the establishment of copulation as the route of transmission for C. penneri between lizards and the discovery of both ecological and physiological host specificity in these worms.This study also provides insight into the host’s biology, specifically support for the female mimicry hypothesis in anoles proposed by Orrell and Jenssen (2003).”
I queried Gabriel Langford, “just how small are these infected males?” He responded: “We sampled an evenly distributed group of females and males that ranged from a few days old to large (male SVL 68mm) adults. If memory serves (I’m on my tablet, no data in front of me), at least 35 of the 87 males fell into the range of 34-50 mm. Also, we had several males just above (infected) and below (uninfected) the 34 mm cut-off, which allowed us to be fairly confident about this number in A. sagrei.”
These results suggest that even quite small males may be mating, even though they are far too small to hold a territory. The idea that “sneaker” males may exist in anole populations has been suggested before, but not demonstrated. The occurrence of such matings has all kinds of interesting implications for anole sexual selection and evolution.
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Liam Revell
I’m somewhat surprised that a male A. sagrei of 34 mm SVL even has fully developed testes. Without reading the Langford et al. paper, isn’t it also possible that these results suggest (perhaps more parsimoniously) that there are just multiple modes of transmission, in addition to copulation, for this parasite?