Natural Egg Mortality of the African Grey Tree Frog, Chiromantis xerampelina (Amphibia: Rhacophoridae)

Abstract

Rainfall patterns are recognised as important for normal ecosystem functioning in arid environments. Most attempts made to understand the effect of rainfall on amphibian ecology have focused on long-term rather than short-term trends. Here, factors effecting embryonic mortality and clutch size of the African foam nesting frog Chiromantis xerampelina were examined at two ponds from April -June in 2011-2012 in Malawi. A total of 73 foam nests were monitored following spawning. On average 29% of eggs in 2011 and 26% in 2012 suffered mortality from both ponds and this mortality significantly varied between nests. Linear regression showed that the date of spawning had a significant effect on mortality due to moisture requirements of the eggs. The height of nests over the water surface had a negative impact on clutch size and increased rainfall decreased egg mortality in both years at both ponds. In a changing climate, with rainfall projected to become more infrequent in this region, organisms may not be able to rely on rainfall patterns as cues for reproduction, which may have a negative impact on amphibian populations. Keywords: Chiromantis; Foam nests; Embryonic mortality; Climate patternsKnowledge on egg and larval survival is essential to understand the population dynamics of amphibians; however, due to the difficulties associated with assessing the survival rate of amphibian embryos and larvae under natural conditions, detailed knowledge of natural survivorship is limited to a few species and populations [1]. Rainfall, oxygen, ultraviolet radiation and temperature can also interact with biotic factors and influence mortality and hatching rate [2][3][4]. Embryos from amphibian egg clutches are surrounded by a protective perivitelline membrane containing perivitelline fluid and a jelly envelope composed of a variable number of layers [5]. Ambient moisture can influence the physical properties and structure of the embryos and the surrounding protective layers and can potentially alter the ability of embryos to hatch. This is particularly important for the many tropical species known to lay their eggs out of the water, thereby exposing their eggs to variable environmental conditions. Annual and seasonal levels of rainfall are projected to change throughout the twenty-first century [6,7] and as a result, mortality of terrestrial amphibian eggs is predicted to increase in the tropics [8,9]. Most studies considering the effect of rainfall on seasonal growth and survival have focused on seasonal or annual weather patterns [10][11][12]; but whereas such large-scale rainfall trends can be useful in explaining community level dynamics [13], they may not reveal the specific mechanisms driving individual mortality. In order to elucidate the effect of short term environmental fluctuations on growth and development, rainfall patterns should be considered on a much shorter timescale [2,14].The African grey tree frog, Chiromantis xerampelina, is a large species of the family Rhacophoridae. Males usually reach 43-75mm and...

Arboreal or terrestrial: Oviposition site of Zhangixalus frogs affects the thermal function of foam nests

“…Thus, the warming effect in terrestrial nests may have protected eggs from this risk. In addition, the contact with moist soil could have eliminated the risk of desiccation (Shangpliang et al., 2020 ), which has been found to be the main factor affecting egg mortality in foam nesting frogs (Allingham, 2017 ; Kusano et al., 2005 ).…”