Soil pH influences embryonic survival in Pseudophryne bibronii (Anura: Myobatrachidae)

Abstract

Abstract: There has been limited research examining the role that terrestrial habitat characteristics play in influencing persistence of amphibian populations. In this study we investigated the influence of a terrestrial habitat attribute on the distribution of the terrestrial egg‐laying toadlet, Pseudophryne bibronii. Eggs of this species are deposited in depressions, or under leaf litter, and develop to a stage where they can hatch to free swimming tadpoles when water covers breeding sites or embryos are washed into water. Because rainfall can be intermittent, eggs may sit for extended periods in terrestrial nests before sufficient rainfall initiates hatching. Appropriate egg‐laying sites must be chosen by both males and females to ensure embryos survive these periods. A study of 20 sites found that soil pH at sites where P. bibronii were recorded as present was significantly lower than pH at sites where P. bibronii were recorded as absent. To determine whether soil pH influenced the hatching success in P. bibronii, experiments were conducted in which batches of eggs were translocated to local areas with different soil pH. Survival rate of eggs was significantly influenced by relatively small changes in pH, with hatching success higher at lower pH. In a laboratory trial survival of eggs raised on sterilized soil was not affected by soil pH. Fungal infection of eggs was observed in the field and laboratory suggesting that hatching success might be affected via a complex interaction between soil pH, fungi and other soil biota. Choice trials using P. bibronii metamorphs indicated that individuals were capable of distinguishing between small differences in pH. Therefore, distribution of P. bibronii may be influenced by either differential mortality of embryos, or habitat choice by post metamorphic individuals, and further experiments are required to determine the relative importance of these factors.