Oviposition and egg mass morphology in barred frogs (Anura: Myobatrachidae: Mixophyes Günther, 1864), its phylogenetic significance and implications for conservation management
Knowles, R, Thumm, K, Mahony, M, Hines, H, Newell, DA & Cunningham, M 2015, 'Oviposition and egg mass morphology in barred frogs (Anura: Myobatrachidae: Mixophyes Günther, 1864), its phylogenetic significance and implications for conservation management', Australian Zoologist, vol. 37, no. 3, pp. 381-402.
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Several species of the Australo-Papuan genus Mixophyes (barred frogs) have declined markedly and are now considered threatened. During field investigations into the possible causes of declines, we observed oviposition and numerous egg masses (700+) of the four species from southeast Australia. From these and published observations there are two markedly different ovipositional processes within Mixophyes. In M. coggeri, M. fasciolatus and M. iteratus eggs are laid in water then deposited terrestrially, propelled from the foot of the floating female onto a near-vertical or overhanging stream bank (Ovipositional Process 1). In M. balbus and M. fleayi eggs are deposited aquatically in the shallow riffle zones of small streams, either into a rounded nest depression in the substrate (Ovipositional Process 2A), or occasionally directly onto bedrock (Ovipositional Process 2B). These observations of ovipositing and egg masses show that there are three reproductive modes in the genus: mode 2 - eggs and exotrophic tadpoles in lotic water (M. fleayi), mode 4 - eggs and early larval stages in constructed basins, exotrophic tadpoles in streams subsequent to flooding – (M. balbus and M. fleayi), and mode 18 (terrestrial eggs above water, exotrophic hatchlings move to water (M. carbinensis, M. coggeri, M. fasciolatus, M. iteratus and M. schevilli). Mixophyes fasciolatus was the only species to use both lentic as well as lotic waters for larval development. For the Australian species amplexus was axillary, occasionally shifting during the process of oviposition to inguinal. Amplexus for the New Guinean M. hihihorlo, is unknown, as is the ovipositional process and reproductive mode. The phylogenetic significance of our observations is that Mixophyes species have non-foamy egg masses, which accords with their recent placement in the family Myobatrachidae. However, no other members of this family show either of the described processes of oviposition, and furthermore we observed amplexus in Mixophyes to be axillary whereas all other reports for myobatrachids are of inguinal amplexus. Our findings have consequences for management of the habitat of barred frogs, three of which are considered threatened. The construction of creek crossings (for vehicles, bikes, horse riding, pedestrians) in riffle zones, the trampling of creek banks by cattle, horses, pigs and humans and changes to the hydrology of creeks by damming or regulating flows that alter the connection between hydrology and stream bank structures, are all likely to have a negative impact on reproductive success.