Chapter 5 Synthesis

University of Groningen On the origin of species assemblages of Bornean microsnails Hendriks, Kasper DOI: 10.33612/diss.124819761 IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2020 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Hendriks, K. (2020). On the origin of species assemblages of Bornean microsnails. University of Groningen. https://doi.org/10.33612/diss.124819761 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 28-09-2021 chapter 5 Synthesis Kasper P. Hendriks Synthesis | 245 Research goal During the past five years I studied the community assembly of Bornean microsnails, and tried to answer the main question: Have Bornean microsnail communities randomly assembled, and if not, what factors were of influence? Because natural ecological communities (especially in the tropics; see below) are such tremendously complex systems (Vellend et al. 2014), I set out on a multi-disciplinary approach to understand better the various community aspects (Figure 5.1). It is one thing to test for community (non-)neutrality to learn how much of an observed pattern can be explained by simple, stochastic processes, but it is additionally interesting to test for (more) deterministic processes (Chase and Myers 2011), such as the influence of community interactions and environmental aspects. I decided to study (i) community composition on habitat islands and to test for neutrality, (ii) phylogeography and demographics to understand possible linkage among island populations and communities, and (iii) individual diets to test for their variation among species and communities. Halfway the project, I decided to add data on (iv) the communities’ environs, and (v) individual microbiomes to test for possible influences of these on diet choice and the overall community. The latter dataset could be added with little additional effort, after I learned that laboratory techniques to obtain these data were very similar to the ones I used to obtain diet data (Box 5.1). Stochastic Deterministic Niche theory Neutral theory Neutral ! ? ? ? direct neutrality diet & phylo- environment tests microbiome geography (SAD) Figure 5.1 The study of ecological communities can take a stochastic approach, such as a direct tests of neutrality, following e.g. the Unified Neutral Theory of Biodiversity (Hubbell, 2001), or a deterministic approach, such as traditionally studied by niche theory (Chase, 2014). In many cases, it is not at all clear if, and how much, can be explained by either deterministic or stochastic processes (such as described by neutral theory), and most likely both are important to some degree. 246 | Chapter 5 Main research findings Schilthuizen (2011) reported that the species abundance distributions (SADs) of Bornean land snail communities follow a logseries-like distribution (Figure 1.3). Using census data from the snail shells we collected from ca. 100 plots, distributed over 15 limestone outcrops in the Lower Kinabatangan Floodplain, we studied the SADs more closely (results presented in Box 5.2). We found that they could generally be fitted well by a neutral model from the Unified Neutral Theory of Biodiversity (UNTB; Hubbell 2001). However, especially at the local scale the most dominant species were more abundant than the model predicts. Pooling community data into a regional pool somewhat ‘evened out’ these extremes. Our phylogeographic and demographic analyses highlighted the highly segregated gene pools in three target snail species- complexes within the region (Chapter 2). Local populations were usually old (> 500,000 years) and often originated from long-distance dispersal (LDD). These findings thus support the application of the UNTB, which assumes neutral community assembly to result, among others, from dispersal limitation. With regard to the influence of traits (niche theory), we did not find support for a direct correlation between plant diet diversity and snail consumer community diversity, although both these communities were positively (though not strongly) correlated to a third community: that of the snail microbiome (Chapter 3). We show that correlations between these three communities may be the result of similar responses to environmental variables. Most notably, consumer and diet diversities correlated negatively with distance to anthropogenic activities (such as plantations and villages), and positively with distance to the nearest cave entrance, which might have an influence as a potential source of nutrients from guano runoff. Consumer community and microbiome diversities both correlated positively with habitat island size, which is in general agreement with the Island Biogeography Theory (MacArthur and Wilson 1967). Snail plant diet richness, a trait that is potentially strongly associated with non-neutral species interactions, differed significantly among the species we studied, but we also found a significant positive correlation with snail size (Chapter 4). From these results, we cannot conclude that the snail diet is dictated by niche partitioning, as larger snails are expected to show a richer diet simply from random feeding with larger mouthparts. While many individual snails showed a sign of a phylogenetic selection of plant diet items, suggesting individual snails have (strong) dietary preferences, we cannot be certain that these results are not the by-product of other, outside-community, selection pressures, such as snails hiding underneath specific plants from predators, and only eating from these locations. Synthesis | 247 Box 5.1 Sampling the diet and microbiome from Bornean microsnail guts. This box’ contents are an edited, summarized version of our research report as published in The Malacologist, newsletter of The Malacological Society of London (Hendriks et al. 2019b). Introduction In the light of our interest in seemingly neutral communities of land snails on limestone outcrops in the Lower Kinabatangan Floodplain in Sabah (Schilthuizen 2011), Malaysian Borneo, we set up a project to study possible influences of traits on the community assembly. More specifically, we applied modern metabarcoding techniques that allow the reconstruction of snail diet and gut microbiome based on genetic data (Pompanon et al. 2012, Taberlet et al. 2012). With these data we tried to answer the question of whether the snail diet and/or microbiome influence the assembly of the species into communities (see Chapters 3 and 4). Methods We visited the Lower Kinabatangan Floodplain in November 2017. Our goal was to resample plots from which we had gathered community data (shells) during visits in 2015 and 2016, so that we could correlate newly gathered diet and microbiome data to previously gathered community data. We visited seven different limestone outcrops within the Lower Kinabatangan Floodplain. From each outcrop, samples were taken from three plots (four in a single outcrop, Keruak) along the base of the outcrop, with a between-plot distance of 50 m (sometimes more if not possible otherwise due to too dense vegetation). Plots measured two by two metres (Figure 5.2). We focussed on three target species of unrelated gastropod: Plectostoma concinnum (Fulton, 1901), Georissa similis E. A. Smith, 1893 s.l.1, and Alycaeus jagori Von Martens, 1859. Studies using standardised plots along a transect that spans both limestone and non-limestone substrate have shown that the prosobranch microsnail genera Plectostoma and Georissa tend to occur nearly strictly on limestone (Schilthuizen et al. 2003a), while Alycaeus was found also away from limestone, but in very low numbers (personal observations). We aimed to collect 40 individuals per target species per plot, with 1 Georissa similis E. A. Smith, 1893 was, until recently, considered a single species, endemic to the Kinabatangan Floodplain. Hendriks et al. (2019a) suggested, based on phylogeographic studies, that the taxon could best be treated as a species-complex, characterized by high levels of endemism due to many long-distance colonization events. Recent taxonomic research by Khalik et al. (2019), based on combined phylogenetic and conchological studies, also suggests that the taxon is in fact best treated as a complex of closely related species: G. flavescens (found along the Kinabatangan River at limestone outcrops Pangi, Keruak, Tomanggong Besar, and Tomanggong 2), G. bangueyensis (widely distributed over northern and eastern Sabah), G. nephrostoma (along the Kinabatangan River on outcrops Keruak and Tandu Batu), G. xesta (widely distributed over Sabah), and G. similis (widely distributed over eastern Sabah). The samples used in the current study were identified as general G.‘ similis s.l.’ only. Because G. similis

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