Rapid differentiation of sexual signals in invasive toads: call variation among populations.

Advertisement calls tend to differ among populations, based on morphological and environmental factors, or simply geographic distance, in many taxa. Invasive cane toads (Rhinella marina) were introduced to Australia in 1935 and their distribution has expanded at increasing rates over time. Rapid evolution occurred in morphological and behavioural characters that accelerate dispersal, but the effects of rapid expansion on sexual signals have not been examined. We collected advertisement calls from four populations of different ages since invasion, and analysed the geographic differentiation of seven call parameters. Our comparisons indicate that the calls of R. marina differ among Australian populations. The signal variation was not simply clinal with respect to population age, climate, or morphological differentiation. We suggest that selection on signalling among populations has been idiosyncratic and may reflect local female preferences or adaptation to environmental factors that are not clinal such as energy availability.

Determinants of the pathways of litter chemical decomposition in a tropical region.

Litter decomposition is a key ecosystem process, yet our understanding of the drivers in chemical changes in leaves during decay is limited. Our aim was to determine the comparative differences (chemical divergence or convergence) between sites and the drivers of decay pathways. We used the litterbag method ('in situ' litterfall and standardized 'control' leaves) in Australian tropical rainforests and near-infrared spectrometry to show the chemical pathways during decomposition (c. 360 d; 12 control sites; 17 in situ sites). Chemical convergence/divergence was determined from spectral dissimilarity and quantile regression along a mass loss moving average. The influence of environment (climate and soil) and litter quality on decay pathways was determined between sites using correlation analysis. Throughout the region, litter composition in both treatments converged chemically during decay. However, divergent chemical pathways were shown for some samples/sites (especially with high initial lignin, phenolics and carbon (C), poor soil phosphorus (P), sodium (Na) and more seasonal moisture), and the diversity of decay residues increased with mass loss despite overall chemical convergence. Our study suggests that there is general chemical convergence of leaf litter during early decay, but also that divergent chemical pathways occur in locations that experience more intense seasonal drying, and contain species or conditions that promote poor-quality litter.