Abstract
While across the animal kingdom offspring are born smaller than their parents, notable exceptions exist. Several dipteran species belonging to the Hippoboscoidea superfamily can produce offspring larger than themselves. In this essay, the blood-feeding tsetse is focused on. It is suggested that the extreme reproductive strategy of this fly is enabled by feeding solely on highly nutritious blood, and producing larval offspring that are soft and malleable. This immense reproductive expenditure may have evolved to avoid competition with other biting flies. Tsetse also transmit blood-borne parasites that cause the fatal diseases called African trypanosomiases. It is discussed how tsetse life history and reproductive strategy profoundly influence the type of vector control interventions used to reduce fly populations. In closing, it is argued that the unusual life history of tsetse warrants their preservation in the areas where human and animal health is not threatened.
Highlights
We focus on the causes and consequences of producing relatively large offspring in tsetse flies, as there are extensive data on their ecology and life history and because of their capacity to transmit the fatal diseases known as the African trypanosomiases
This essay describes how several species within the blood-feeding Hippoboscoidea superfamily are clear exceptions to the juvenile small size (JSS) principle, which is best illustrated by tsetse flies birthing offspring larger than themselves
We are focusing on tsetse flies because these long-lived, free-living flies are restricted to the African continent and are vectors of a parasite causing harm to humans, livestock, and wildlife
Summary
The short gestation period of tsetse flies (relative to their lifespan) approximates to that of small, viviparous vertebrates such as mammals,[28] when, in comparison, larger vertebrates have longer relative gestation periods. Like all members of the Cyclorrhapha, tsetse flies produce a larva that, being soft and malleable in form, can be readily squeezed out of the birth canal, despite the larva being as large as its mother (Figure 2).[22] We see in this mechanical consideration why it is that the reproductive strategy of tsetse flies can be so different from that of species with physiological restrictions. To compare this feature with more familiar creatures, even dedicated carnivores feeding on a protein-rich diet could not deliver a giant baby through the pelvic girdle. There is only a weak correlation between birth size and the channel width of any pelvic girdle,[10] adaptations to viviparity include uniquely modified reproductive morphologies such as a vagina that is more muscular and tracheated (ridged).[13]
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