Offspring size variation in a hybrid zone of Australian frogs (Geocrinia laevis complex, Myobatrachinae)

Abstract

To describe variation in size of offspring across a hybrid zone between the myobatrachine frogs Geocrinia laevis and Geocrinia victoriana, the sizes of tadpoles hatching from egg masses collected in the field were measured. Hatchling size was strongly correlated with diameter of the blastula or gastrula (referred to here as "egg size"). Geocrinia victoriana had bigger offspring than G. laevis. Hybrids were generally intermediate between the two parental species in offspring size. However, the variation in size across the hybrid zone did not show a smooth cline or a distinct step coinciding with any of the sharp transitions found for behavioural or genetic characters. Variation within hybrid populations was not greater than in "pure" samples of the two species; these data correspond to findings of other studies which showed that this contact between G. laevis and G. victoriana is a "true hybrid zone" with panmictic local populations, not an overlap of the two species.

A comparative study of divergent embryonic and larval development in the Australian frog genus Geocrinia (Anura: Myobatrachidae)

“…Newly hatched tadpoles of G. victoriana are slightly larger than those of G. laevis, also reported by Gollmann and Gollmann (1994), and similarly slightly larger than G. leai. Hatched tadpoles of G. victoriana showed reductions in dry mass, total length, tail fin length and fin height when reared out of water, compared with those reared in hydrated situations which grew larger Andrewartha et al (2008).…”

“…Apart from slight exceptions noted below, the eyes of most larvae are lateral in life. Gollmann and Gollmann (1994) reported some slight geographical variation in the eye position of G. victoriana tadpoles, and tadpoles of G. leai in the current study also show slight variation in eye position between northern and southern coastal populations ( Figure 5). In dorsal view, the body shape of live members of both the G. laevis and G. rosea groups is similar (after about stage 29 in the latter) and in lateral view, the tail shape is generally similar.…”

Microevolution and maternal effects on tadpole Rana temporaria growth and development rate

“…Some other studies have yielded similar results. In a study by Parichy & Kaplan (1992), initially small tadpoles (Bombina orientalis) presumably hatched from small eggs (Williamson & Bull, 1989;Gollmann & Gollmann, 1994;Parichy & Kaplan, 1995), grew and developed similarly to large larvae when raised under good food conditions. However, when raised under poorer food conditions they metamorphosed later and at a smaller size.…”