Frogs without polliwogs: Evolution of anuran direct development

Abstract

Direct development is the assumption of the adult morphology without progression through an intervening, morphologically distinct, free-living larval phase. We discuss the ecological factors contributing to the evolution of this derived life-history strategy in frogs, and the developmental modifications that facilitate such an unusual mode of embryogenesis. Studies on the Puerto Rican tree frog, Eleutherodactylus coqui, have identified several such modifications, including developmental adaptations for dealing with increased egg size, and loss of tadpole structures. Surprisingly, this direct developer still undergoes a thyroid hormone-dependent metamorphosis, which occurs before hatching. We suggest how the ancestral biphasic developmental pattern may have been rearranged during the evolution of direct development.

Cenozoic biogeography and evolution in direct-developing frogs of Central America (Leptodactylidae: Eleutherodactylus) as inferred from a phylogenetic analysis of nuclear and mitochondrial genes

“…Many frog communities are dominated by Eleutherodactylus, both in terms of diversity and abundance (Lieberman, 1986;Scott, 1976), especially those in the highlands (Doan and Arriaga, 2002;Hofer and Bersier, 2001). This genus possesses an unusual, though not unique, mode of development among anurans in which the tadpole stage has been lost, eggs are laid terrestrially, and the young hatch out as tiny froglets (Callery et al, 2001;Elinson et al, 1990). Because of its direct development, Eleutherodactylus has provided a model system for studies of the evolution of development (Elinson and Ninomiya, 2003;Hanken et al, 2001).…”

Nutritional endoderm in a direct developing frog: A potential parallel to the evolution of the amniote egg

“…Direct measurements of TH across development have not been carried out, but the beginning of endogenous TH production is predicted to be around TS 11, just after the thyroid gland forms (Jennings and Hanken, 1998) and when TH-dependency begins (Callery and Elinson, 2000;Callery et al, 2001). The peak histological activity of the thyroid gland and beginning of tail resorption occurs at TS 13 (Jennings andHanken, 1998, Townsend andStewart, 1985), suggesting the peak of endogenous TH titer at this stage.…”

Kowalevsky, comparative evolutionary embryology, and the intellectual lineage of evo‐devo

“…The results are appearing from a number of contemporary laboratories, including (in hardly an exhaustive list) studies of ascidians (Jeffery et al,'99), amphioxus (Holland, 2002), hemichordates (Takacs et al, 2002;Lowe et al, 2003), a swarm of arthropods (Hughes and Kaufman, 2002), nematodes (Sommer, 2000), fish (Parichy and Johnson, 2001;Yamamoto et al, 2003), frogs (Callery et al, 2001), snakes (Cohn and Tickle, '99), starfish (Hart et al,'97), and sea urchins (Raff, '96;Wray, 2000). All of these systems offer particular advantages in addressing specific problems in the evolution of development, such as the role of Hox genes in the evolution of body form.…”