Climatic Correlates of Breeding, Simultaneous Polyandry and Potential for Sperm Competition in the Frog Crinia georgiana

Quantification of underwater calling and foraging activities in the African clawed frog Xenopus laevis

Aquatic anuran species are difficult to detect and observe and this is a major limit to the study of their behaviour and ecology. This habit limits the direct monitoring of sexual and foraging activity, and the investigation of how environmental factors influence their expression as well as how individuals allocate time between competing activities. We investigated this issue in Xenopus laevis, a mostly aquatic frog that forages and emits calls underwater. This model species in biology has been extensively studied in the lab but its behaviour in nature remains poorly described. We carried out a study in a pond during the breeding season in the French invasive range. We recorded underwater vocal activity as a proxy for sexual activity using a hydrophone, set food-baited traps to quantify foraging activity, and recorded environmental conditions (moonlight intensity, temperature and rainfall) over two lunar cycles. We found that individuals engage in these two activities during the breeding season. At the peak of the breeding period, vocal activity was expressed during the day. The investment in reproduction (calling activity) may reduce the time allocated to foraging on a circadian scale. The two activities seem to be partitioned depending on moonlight intensity, with a stronger effect on males. Foraging activity decreased and vocal activity increased when moonlight intensity increased. We also observed a negative effect of temperature and a positive effect of rainfall on vocal activity only. Our method is promising to monitor the activity of other aquatic anurans.

Sex differences in response to environmental and social breeding cues in an amphibian

The relative influence of climatic and social factors on sex-specific variation in reproductive behaviour remains poorly understood. Here, we examine the influence of multiple climatic cues in combination with a social cue on the reproductive behaviours of males and females in a terrestrial breeding toadlet (Pseudophryne coriacea). Over a 115-day breeding season, arrival patterns of each sex, and male calling activity, were recorded daily, while climatic variables were logged continuously. Multivariate analysis showed that arrival of males at the breeding site, as well as male nightly calling activity, were most strongly influenced by a climatic variable (rainfall). By contrast, female arrival was strongly correlated with a social variable (male calling activity), with abiotic conditions having no influence, other than a moderate influence of lunar phase (lunar illumination). These results suggest that cues used for breeding are sex specific and provide new evidence that combinations of climatic and social cues can be integrated into breeding decisions.

Breeding phenology in Rana temporaria. Local variation is due to pond temperature and population size

Frog breeding phenology in temperate zones is usually compared to progress of spring temperatures at a regional scale. However, local populations may differ substantially in phenology. To understand this, local climate and other aspects must be studied. In this study, breeding phenology of the common frog, Rana temporaria, in a set of ponds in southern Sweden is analyzed. There was within year a variation of up to 3 weeks in start of breeding among local populations. Water temperature was measured in the ponds, and breeding tended to be earlier in warmer ponds (surprise!). Breeding was also earlier in ponds with a large breeding congregation. Alternative reasons for these patterns are suggested and discussed. There was a large residual variation. The common frog has a wide range of acceptable wintering sites, and I hypothesize that the particular choice by a local population may explain part of this residual variation.

Sperm morphology, motility and fertilisation capacity in the myobatrachid frog Crinia georgiana

Sperm traits have been found to vary between individuals within populations in a variety of taxa. Sperm motility, morphometry and viability may be expected to have important effects on male fertility, although previous studies have found varying patterns, especially in external fertilisers. In the present study, we examined the effects of sperm swimming velocity, the proportion of motile spermatozoa, sperm head and tail length and the proportion of live spermatozoa on fertilisation success in the externally fertilising myobatrachid frog Crinia georgiana using IVF techniques and by controlling sperm numbers. We found no effect of any of the sperm traits we measured on IVF success. Neither did we find any relationship between sperm morphology and sperm performance. There was a negative relationship between sperm viability and male body size, which could be a function of age or an alternative tactic of differential investment in spermatozoa by smaller-sized males using sneak tactics in multiple matings. In contrast with most externally fertilising aquatic organisms, high rates of fertilisation appear to be achieved in C. georgiana with relatively low sperm swimming speeds.

Riqueza e densidade de vocalizações de anuros (Amphibia) em uma área urbana de Corumbá, Mato Grosso do Sul, Brasil

A riqueza e intensidade de vocalizações de anuros em uma área urbana de Corumbá, Mato Grosso do Sul, Brasil, foram estudadas de fevereiro de 2002 a Janeiro de 2003 em uma poça temporária. Foi utilizado um transecto com quatro pontos de escuta onde foram consideradas as espécies visualizadas e a intensidade das respectivas vocalizações. Foram registradas 16 espécies de quatro famílias: Bufonidae (2), Hylidae (7), Microhylidae (1) e Leptodactylidae (6). O período reprodutivo dessas espécies esteve correlacionado com a estação chuvosa, de dezembro a março (r² = 0,806, F(1,10) = 41,530 p = 0,002, n = 12). As espécies que apresentaram maior intensidade de vocalização foram Scinax nasicus (Cope, 1862) e Physalaemus albonotatus (Steindachner, 1864), com picos em janeiro. A espécie que apresentou maior período de vocalização foi Leptodactylus fuscus, de setembro a fevereiro. O maior número de espécies e de indivíduos vocalizando ocorreu de 19:00 às 23:00 h.