Freshwater decapod crustaceans serve important ecological functions in tropical stream ecosystems. Stream surveys for decapod crustacean fauna were conducted between February 2015 and April 2016 at nine sites in Bukit Timah Nature Reserve (BTNR). A total of eight species (four freshwater crab, three freshwater shrimp and one crayfish species) out of the nine species known from BTNR were recorded. In general, the species were recorded from sites matching environmental conditions previously known or reported for each species, with some crab species showing minor overlap in their spatial distributions. This highlights the importance of broad-based conservation efforts focusing on the entire stream network in BTNR rather than on specific/selected streams as the various species each appear to have largely unique habitat requirements. The updated information on freshwater decapod crustaceans in BTNR can be used to inform the formulation of conservation and management measures including the establishment of monitoring programs for the protection of our native and threatened aquatic fauna in BTNR.

ABSTRACT. The current paper acts as an introduction to nine following papers concerning the hydrology and biodiversity of Nee Soon freshwater swamp forest. Freshwater swamp forest is a threatened and overlooked ecosystem in the Southeast Asian region and in Singapore. Characterised by predominantly mineral soils supporting forest that contains a subset of the flora and fauna of lowland forest, but with the addition of important habitat specialists, freshwater swamp forest is fed by an array of hydrological processes. As conservation management depends on good hydrological and biological understanding, a research programme was designed to tease out the roles of the various hydrological components. The background, management concerns, and aims of the project are detailed.

Bukit Timah Nature Reserve (BTNR) holds the largest remnant patch of primary rainforest in Singapore and its hill streams supports many native and threatened freshwater fauna. As the last comprehensive survey of freshwater fishes in BTNR was published nearly two decades ago, a series of surveys was carried out at 12 streams permeating BTNR and the Singapore Quarry to update the status of the fishes. Of the 27 species documented, 16 are native to Singapore and 11 are introduced. Two native species known from other parts of the Central Catchment Nature Reserve are recorded for the first time in BTNR. Species distribution, richness and abundance have been qualitatively assessed in relation to habitat characteristics. Potential threats and mitigation measures are discussed, which are important in the formulation of conservation and management strategies to safeguard the current diversity of freshwater fishes, many of which are threatened in rapidly developing Singapore.

ABSTRACT. Nee Soon freshwater swamp forest is the last remaining primary freshwater swamp forest left in Singapore and it contains a rich diversity of native and locally threatened fauna. As native terrestrial snails and slugs are poorly studied and understood in Nee Soon freshwater swamp forest, an extensive survey was conducted to establish their current status. A total of 19 species was recorded, of which one was recorded for Singapore for the first time. Amphidromus atricallosus temasek, a recently described subspecies endemic to Singapore, was found to be more commonly distributed than previously known from the swamp forest. Results also indicate that despite low overall abundance, Nee Soon freshwater swamp forest harbours a rich diversity of land snails and slugs. Any future long term changes in climate or topography, or short term changes in hydrology, might affect their distribution and diversity.

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Species radiations have long fascinated biologists, but the contribution of adaptation to observed diversity and speciation is still an open question. Here, we explore this question using the clove genus, Syzygium, the world’s largest genus of tree species comprising approximately 1200 species. We dissect Syzygium diversity through shotgun sequencing of 182 distinct species and 58 additional as-yet unidentified taxa, and assess their genetic diversity against a chromosome-level reference genome of the sea apple, Syzygium grande. We show that Syzygium grande shares a whole genome duplication (WGD) event with other Myrtales. Genomic analyses confirm that Syzygium originated in Sahul (Australia-New Guinea), and later diversified eastward to the Hawaiian Islands and westward in multiple independent migration events. The migrations were associated with bursts of speciation events, visible by poorly resolved branches on phylogenies and networks, some of which were likely confounded by incomplete lineage sorting. Clinal genomic variation in some sublineages follows phylogenetic progression, which coupled with sympatric occurrences of distantly related species suggests that both geographic and ecological speciation have been important in the diversification of Syzygium. Together, these results point to a mixture of both neutral and adaptive drivers having contributed to the radiation of the genus.