Explore the vast range of titles available.

High background noise is an impediment to signal detection and perception. We report the use of multiple solutions to improve signal perception in the acoustic and visual modality by the Bornean rock frog, Staurois parvus. We discovered that vocal communication was not impaired by continuous abiotic background noise characterised by fast-flowing water. Males modified amplitude, pitch, repetition rate and duration of notes within their advertisement call. The difference in sound pressure between advertisement calls and background noise at the call dominant frequency of 5578 Hz was 8 dB, a difference sufficient for receiver detection. In addition, males used several visual signals to communicate with conspecifics with foot flagging and foot flashing being the most common and conspicuous visual displays, followed by arm waving, upright posture, crouching, and an open-mouth display. We used acoustic playback experiments to test the efficacy-based alerting signal hypothesis of multimodal communication. In support of the alerting hypothesis, we found that acoustic signals and foot flagging are functionally linked with advertisement calling preceding foot flagging. We conclude that S. parvus has solved the problem of continuous broadband low-frequency noise by both modifying its advertisement call in multiple ways and by using numerous visual signals. This is the first example of a frog using multiple acoustic and visual solutions to communicate in an environment characterised by continuous noise.

Background Female frog-biting midges ( Corethrella ) are hematophagous micropredators that feed on frogs and serve as vectors for trypanosomes ( Trypanosoma ), unicellular flagellate parasites. Little is known about the infection ecology and host specialization within this tritrophic interaction. Methods In this study, we explore the prevalence, diversity and specificity of Trypanosoma infections in Corethrella across various localities in tropical America and Borneo by sequencing both midge and trypanosome markers in midge samples. Results Bayesian phylogenetic analyses and ASAP species delimitation of Corethrella (cytochrome c oxidase I [COI]) and Trypanosoma (18S, glyceraldehyde 3-phosphate dehydrogenase [GAPDH]) revealed a previously unknown high diversity of frog-biting midge-associated trypanosomes. Across regions and localities, the infection prevalence in midges caught by acoustic midge traps ranged from 2.9% to 23.5%, suggesting that a notable proportion of midges carried trypanosomes, likely acquired from a previous blood meal. At one locality, La Gamba (Costa Rica), the infection prevalence in trap-caught midges was 10.9%, while it was even higher in midges collected directly from frog hosts (20.7%), in agreement with the hypothesis that midges ingest trypanosomes from infected frogs. Bipartite network analyses revealed high degrees of specialization of Trypanosoma in trap-caught Corethrella, both across all localities (H2′ = 0.87) and when analyzed for our most sampled locality (Cahuita, Costa Rica) alone (H2′ = 0.94). Conclusions Our data suggest that most trypanosomes detected in trap-caught midges are established, host-competent (i.e., specialist) parasites in an infective stadium. Graphical Abstract

Most birds are characterized by a seasonal phenology closely adapted to local climatic conditions, even in tropical habitats where climatic seasonality is slight. In order to better understand the phenologies of resident tropical birds, and how phenology may differ among species at the same site, we used ~70 000 hours of audio recordings collected continuously for two years at four recording stations in Singapore and nine custom‐made machine learning classifiers to determine the vocal phenology of a panel of nine resident bird species. We detected distinct seasonality in vocal activity in some species but not others. Native forest species sang seasonally. In contrast, species which have had breeding populations in Singapore only for the last few decades exhibited seemingly aseasonal or unpredictable song activity throughout the year. Urbanization and habitat modification over the last 100 years have altered the composition of species in Singapore, which appears to have influenced phenological dynamics in the avian community. It is unclear what is driving the differences in phenology between these two groups of species, but it may be due to either differences in seasonal availability of preferred foods, or because newly established populations may require decades to adjust to local environmental conditions. Our results highlight the ways that anthropogenic habitat modification may disrupt phenological cycles in tropical regions in addition to altering the species community.

Nepenthes pitchers are specialized leaves that function as insect traps. Several pitcher components may contribute to trapping, including the pitcher fluid, slippery wax crystals and downward-pointing epidermal cells on the inner pitcher wall, and the wetness-dependent pitcher rim (peristome), but the relative importance of these traits is unclear. Mechanisms of prey capture and retention in the field were investigated by quantifying the effect of 'knock-out' manipulations of individual pitcher structures, and by testing the ability of pitcher fluids and water to retain insects. Two forms of Nepenthes rafflesiana Jack ('elongate' and 'typical') with contrasting combinations of pitcher traits were compared. Wax crystals on the inner pitcher wall were found to be the most important trapping structure in the elongate form, whereas the typical form relied primarily on the peristome. The pitcher fluids of both forms, differing markedly in the degree of viscoelasticity, retained significantly more ants than water. The present results show that pitcher plants utilize several mechanisms for prey capture and retention, varying in efficiency and relative importance between forms. It is proposed that these differences represent alternative prey capture strategies that may provide a mechanism to reduce competition and facilitate species co-existence in nutrient-limited habitats.

Species with separate sexes (dioecy) are a minority among flowering plants, but dioecy has evolved multiple times independently in their history. The sex‐determination system and sex‐linked genomic regions are currently identified in a limited number of dioecious plants only. Here, we study the sex‐determination system in a genus of dioecious plants that lack heteromorphic sex chromosomes and are not amenable to controlled breeding: Nepenthes pitcher plants. We genotyped wild populations of flowering males and females of three Nepenthes taxa using ddRAD‐seq and sequenced a male inflorescence transcriptome. We developed a statistical tool (privacy rarefaction) to distinguish true sex specificity from stochastic noise in read coverage of sequencing data from wild populations and identified male‐specific loci and XY‐patterned single nucleotide polymorphsims (SNPs) in all three Nepenthes taxa, suggesting the presence of homomorphic XY sex chromosomes. The male‐specific region of the Y chromosome showed little conservation among the three taxa, except for the essential pollen development gene DYT1 that was confirmed as male specific by PCR in additional Nepenthes taxa. Hence, dioecy and part of the male‐specific region of the Nepenthes Y‐chromosomes likely have a single evolutionary origin.

In many species that use acoustic signals for mate attraction, males are usually the most vocal sex. In frogs, females typically remain silent, while males produce advertisement calls to attract mates. In some species, females vocalize, but usually as a response to an initial male advertisement call. The smooth guardian frog (Limnonectes palavanensis), found on Borneo, has exclusive paternal care while the females mate and desert after laying the clutch. Males provide care to the eggs until hatching and then they transport the tadpoles to small bodies of water. The vocal repertoire of this species has never been described. Males have a distinctive advertisement call to at tract females, but produce the call very infrequently. We found that females of L. palavanensis not only respond to male advertisement calls but also vocalize spontaneously, forming lek-like aggregations around a single male. Males may or may not respond to a particular female with a short courtship call, which is elicited only by the female call and not the male advertisement call. The calling rate of females is consistently higher throughout the night compared with the calling rate of males. These observations suggest that this species exhibits a reversal in calling behavior and possibly a sex-role-reversed mating system.

1. Beneficial 'services' in mutualistic interactions have often not evolved de novo, but from ancestral traits that had a function before the emergence of the association. These traits can then acquire novel functions in a mutualism. Even in many close insect-plant relationships, the services provided by each partner are still unclear. 2. In the well-known association between the carnivorous pitcher plant, Nepenthes bicalcarata, and Camponotus schmitzi ants in Borneo, the ants benefit by receiving food and nesting space in swollen, hollow pitcher tendrils, but the benefits to the plant are less clear. Previous studies have suggested that the ants protect against herbivory, prevent putrefaction of pitchers by removing prey items from them or increase the pitcher's prey retention rate by attacking pitcher visitors. 3. Field observations showed that C. schmitzi ants regularly clean the pitcher rim (peristome), which is the main surface responsible for prey capture. We found that this behaviour increases the carnivorous plant's prey capture efficiency and helps to maintain it over the pitcher's life span. Running tests with Oecophylla smaragdina ants on colonised and ant-free older pitchers demonstrated 45·8% higher capture efficiency in pitchers inhabited by C. schmitzi. Head counts of trapped ants showed that C. schmitzi-colonised pitchers indeed captured significantly (45·2%) more prey than uncolonised pitchers of the same age. 4. The peristomes of ant-free older pitchers were strongly contaminated by fungal hyphae and other particles. Experimental contamination of clean pitcher peristomes with starch also strongly reduced capture efficiency. While the peristome was cleaned rapidly in ant-colonised pitchers and capture efficiency returned to the previous level within approximately 1 week, no cleaning and recovery were observed in ant-free pitchers. 5. Within the genus Nepenthes, N. bicalcarata has exceptionally long-lived pitchers. We propose that C. schmitzi ants benefit N. bicalcarata by keeping the pitchers effective over long periods of time, likely allowing the plant to acquire more nutrients per pitcher and thereby minimise pitcher construction costs. 6. Our findings demonstrate that the cleaning behaviour typical of many plant-ants has acquired a novel function in this ant-plant association, giving rise to a new type of myrmecotrophic mutualism.

The conversion of tropical rain forests to oil palm plantations is a major threat to Southeast Asia's rich biodiversity. Fostering forest species communities in secondary forests, agroforestry systems, and plantations is therefore increasingly becoming a conservation focus. This study uses standardized transect‐based sampling to compare species richness, density and community composition of stream anuran assemblages among primary forests, repeatedly logged forests and oil palm plantations in northern Borneo. In primary forest streams, we recorded an average of 19 frog species, compared to 15 species in logged forests and 11 species in oil palm plantation streams. However, the high percentage of canopy cover above the plantation streams mitigated this loss to some extent. This study corroborates numerous studies that oil palm plantations have mainly negative effects on the region's biodiversity. However, our results also demonstrate the high conservation value of logged forests for Bornean stream‐dependent anurans. We conclude that palm plantations have a largely unused potential to promote regional anuran biodiversity.

1. Mutualisms are interspecific interactions where each of the species involved gains net benefits from the other(s). The exchange of resources and/or services between mutualistic partners often involves tasks that species originally accomplished themselves but which have been taken over by or transferred to the more efficient partner during the evolution of the mutualism. Such 'ecological outsourcing' can be seen, for example, in several carnivorous plants that have transferred prey capture and digestion to animal partners. However, the outcome of this transfer and its fitness relevance has rarely been quantified. 2. Using a digestive mutualism between a carnivorous pitcher plant (Nepenthes hemsleyana) and a bat (Kerivoula hardwickii) as a model, we tested the hypothesis that ecological outsourcing is a profitable strategy for the outsourcing partner. To evaluate the value of this mutualism, we conducted a series of field and glasshouse experiments. We measured the benefits of ecological outsourcing by comparing survival, growth, photosynthesis and nutrient content of N. hemsleyana plants fed with bat faeces to those fed with arthropods. To investigate the costs of such outsourcing processes, we repeated the experiment with the closest relative (Nepenthes rafflesiana) that is not adapted to digest bat faeces. 3. We found that N. hemsleyana plants fed with faeces had increased survival, growth and photosynthesis compared to plants fed with arthropods only. On average, plants covered 95% of their nitrogen demand from faeces under strong nutrient deprivation. Despite N. rafflesiana's higher arthropod capture rate, faeces covered a large part of this species' nutrient demand as well, suggesting low costs for outsourcing. 4. Synthesis. Outsourcing prey capture and digestion to the mutualism partner seems to be a beneficial strategy for N. hemsleyana. It may explain the evolutionary trend of several carnivorous plants to lose their carnivorous traits while increasing their attractiveness to mutualistic partners. On a much broader scale, we propose that ecological outsourcing could be one of the major drivers for the evolution and maintenance of mutualisms.

Carnivorous pitcher plants capture prey with modified leaves (pitchers), using diverse mechanisms such as 'insect aquaplaning' on the wet pitcher rim, slippery wax crystals on the inner pitcher wall, and viscoelastic retentive fluids. Here we describe a new trapping mechanism for Nepenthes gracilis which has evolved a unique, semi-slippery wax crystal surface on the underside of the pitcher lid and utilises the impact of rain drops to 'flick' insects into the trap. Depending on the experimental conditions (simulated 'rain', wet after 'rain', or dry), insects were captured mainly by the lid, the peristome, or the inner pitcher wall, respectively. The application of an anti-slip coating to the lower lid surface reduced prey capture in the field. Compared to sympatric N. rafflesiana, N. gracilis pitchers secreted more nectar under the lid and less on the peristome, thereby directing prey mainly towards the lid. The direct contribution to prey capture represents a novel function of the pitcher lid.