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The maritime trap-jaw ant Odontomachus malignus Smith, 1859 is thought to be widespread throughout islands in the Indo-Pacific and parts of the Oriental realm. Because of its unique nesting preference for harsh littoral habitat and distinct morphology, O. malignus has usually been assumed to consist of only one species. We, however, describe a new species similar to O. malignus found in the mangroves of Singapore, Southeast Asia – Odontomachus litoralissp. nov. We find strong evidence of both species existing in (near) sympatry, and also distinct morphological differences between O. malignus and the new species. Additional complementary DNA evidence in the form of COI barcodes (313 bp) supporting putative species identification and delimitation is provided. Defining morphological characteristics for the O. malignus species group (nested within the larger O. infandus clade) are given in detail for the first time. The worker and queen castes of the new species are described; a redescription of the worker caste of O. malignus, based on specimens from Singapore and the Philippines in addition to the holotype, is also given. The males of both species are also described for the first time, including male genitalia. A preliminary key to most known species of the O. infandus group based on the worker caste is provided.

South-east Asian apple snails, Pila spp., have been declining since the introduction of globally invasive, confamilial South American Pomacea spp., yet Pila ecology remains poorly studied, with most occurrence records unconfirmed. Pila scutata, a previously widespread species, presumed native to the Malay peninsula and assessed as Least Concern in the IUCN Red List, was formerly harvested for food, and may have experienced anthropogenic translocations. We surveyed the Malay peninsula (specifically Peninsular Malaysia and Singapore) to investigate the current distribution and genetic diversity of P. scutata. Six populations were found in Singapore, but only one in Peninsular Malaysia. Mitochondrial COI and 16S sequencing revealed that the Malaysian population shared a single haplotype of both genes with the Singapore populations (500 km distant). This low genetic diversity could stem from a recent anthropogenic introduction, which brings into question the true native range of P. scutata and, coupled with poorly resolved taxonomy of the genus, necessitates a reassessment of its IUCN Red List status. Introduced populations pose a dilemma, and the lack of genetic diversity is of concern in light of Pila decline throughout South-east Asia. Our results highlight that conservation management of P. scutata and its congeners must therefore be better informed by greater taxonomic resolution and more comprehensive investigations of their ecology, both in native and introduced ranges.

Biologists frequently sort specimen-rich samples to species. This process is daunting when based on morphology, and disadvantageous if performed using molecular methods that destroy vouchers (e.g., metabarcoding). An alternative is barcoding every specimen in a bulk sample and then presorting the specimens using DNA barcodes, thus mitigating downstream morphological work on presorted units. Such a "reverse workflow" is too expensive using Sanger sequencing, but we here demonstrate that is feasible with an next-generation sequencing (NGS) barcoding pipeline that allows for cost-effective high-throughput generation of short specimen-specific barcodes (313 bp of COI; laboratory cost

Carnivorous plants avoid below-ground competition for nitrogen by utilizing an alternative nitrogen resource—invertebrate prey, but it remains unclear if sympatric carnivorous plants compete for prey resources. The aim of this study was to investigate if exploitative prey-resource competition occurs between the two sympatric pitcher plant species, Nepenthes rafflesiana and N. gracilis in Singapore. We first investigated if prey-resource partitioning occurs between these two species, and then investigated niche shift in N. gracilis by examining its pitcher contents along an in situ gradient of N. rafflesiana interspecific competition. Our results showed clear evidence of resource partitioning between the two species, but contrary to the expectation of competition, proximity to N. rafflesiana pitchers correlated with higher total prey numbers in N. gracilis pitchers. Our multivariate model of prey assemblages further suggested that N. rafflesiana facilitates N. gracilis prey capture, especially in several ant taxa that are trapped by both species. Concurrently, we found strong evidence for intraspecific competition between N. gracilis pitchers, suggesting that prey resources are exhaustible by pitcher-predation. Our results show that resource partitioning can be associated with facilitative interactions, instead of competition as is usually assumed. Facilitation is more typically expected between phylogenetically distant species, but divergences in resource acquisition strategies can permit facilitation between congeners.

Various crab taxa are known to use their external colouration as visual courtship signals. Early research on the mangrove crab Parasesarma peninsulare Shahdadi et al., 2018 indicated a potential role in sexual signalling for its bright blue-green facial bands, which are highly conspicuous against mangrove mud. To advance this work, we conducted experiments investigating both male responses to female stimuli and female responses to male stimuli. Two sets of binary choice experiments were performed—one with live crabs and one using androgyne images where the only sex-specific cue was facial band colour—to test whether the crabs could distinguish between male and female conspecifics based on the colour of their facial band alone, i.e. independent of auditory, chemical and other visual cues. In both cases, the crabs showed a significantly greater preference for conspecifics of the opposite sex (i.e. males preferred females and vice versa). These results provide evidence for colour vision in Parasesarma and suggest that the facial bands are used by the crabs for sexual discrimination and mate recognition.

The conversion of natural habitats to croplands is a major cause of the global loss of species diversity and ecosystem services. One potentially effective method for enhancing the biodiversity of important groups such as insects, and their associated ecosystem services within croplands, is to increase the environmental complexity of the agricultural matrix. This can be achieved in perennial tree crops by planting mixed-age stands. There is, however, very little evidence for the effects of stand age on biodiversity in tropical tree crops. In this study, we assess how ground-foraging ant communities differ in relation to oil palm stand age, currently the dominant tree crop across tropical Southeast Asia. Oil palm age did not affect overall ant species richness. However, the numbers of species that were either common or numerically-dominant decreased with increases in canopy cover, which positively correlated with oil palm age, suggesting greater species evenness in older oil palm. In mature, but not young, oil palm, ant species co-occurred non-randomly, suggesting competitive exclusion and species segregation. Species responses to variables associated with oil palm age depended on their functional group. Generally, opportunists and generalized myrmicines were less abundant and less diverse, whereas specialist predators were more abundant and diverse, in older oil palm. Our results show that ground-foraging ant communities in oil palm change significantly in composition, but not in species richness, with crop age. These results suggest that mixed-age stands could support compositionally variable communities and help boost insect diversity in otherwise homogeneous perennial monocultures.

The true diversity of the Asian ant genus Rhopalomastix Forel is poorly understood. We use an integrated approach to review the known species and subspecies of Rhopalomastix in Southeast Asia. Based on morphology and supporting DNA evidence, we recognize six species. We raise two subspecies of R. rothneyi Forel to species rank ( R. johorensis Wheeler stat. n, R. javana Wheeler stat. n.), synonymize R. janeti Donisthorpe (syn. nov.) with R. johorensis , and describe four new species from Singapore: R. glabricephala sp. n., R. murphyi sp. n., R. striata sp. n., and R. tenebra sp. n. All six species found in Southeast Asia are distinct from each other based on morphology; morphological delimitation of these species is further supported by and congruent with mOTUs generated from objective clustering of short fragment COI barcodes using the best close match criteria. Different castes and sexes of most species are described, including redescriptions of the queen of R. javana and male of R. johorensis . A key to the Southeast Asian species based on the worker caste is also provided. Variation among sympatric and also geographically distant populations, and the possibilities of cryptic species, are discussed.