Sunday

Sexual Dimorphism Troubles


Meet the Forest Rain Frog (Breviceps sylvestris) discovered in 1930. It is endemic to the Limpopo Province of north-eastern South Africa, where it has two sub-populations separated by 80 km of unsuitable habitat. It lives at 800-1,800 km above sea level, making it a highland species. It is on the IUCN Red List as endangered due to habitat fragmentation; in this case more than half of the total individuals in the species live in isolated patches. It is a small frog, ranging from 2-10cm long (snout-ventral length). They are fossorial (living underground), and as such have adapted to walking and digging rather than hopping or swimming; their hind limbs are too reduced for either of these modes of locomotion.

But, what makes this frog really amazing is how it mates. The mating occurs in underground chambers dug by the female. This isn’t too unusual. The odd part is that the female is significantly larger than the male. This presents a problem in that the male cannot clasp his forelimbs around her body to mate with her. The solution: glue. The male secretes a natural glue on his stomach and attaches himself to the back of the female. At this point he is attached to her and can fertilize the eggs once they are in the underground chamber she has dug. The eggs hatch into fully formed frogs, the tadpole (larval) stage occurring within the egg. This helps reduce the number of offspring lost to predations during the transition from the larval to adult stage.

The diagram shows typical frog mating positions with the center diagram being the Forest Rain Frogs. The male is grey, the female white.

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