hybridization

Abstract  Corals provide habitat for numerous marine species and ecosystem services for global human populations. However, they are vulnerable to local and global scale threats, especially climate change. Measuring demographic processes such as dispersal and ecological processes such as niche partitioning are important for predicting their responses to disturbances and environmental change. So far, correlations between coral genetics and the environment or spatial scale have largely been made over large habitat distinctions, such as depth, reef zone, and among islands or geographic regions. Reefs comprise structurally heterogenous landscapes and thus microhabitats may vary considerably, however, we have little understanding of how genotypes are distributed within reefs across fine spatial scales. Dynamics at fine spatial scales are particularly important in corals due to the frequent discovery of genetically divergent but morphologically indistinguishable coral taxa found sympatrically within reefs (i.e., cryptic taxa, often with no obvious environmental distinctions) and evidence that dispersal distances may be small for some taxa. Technological advancements in both genomic sequencing and underwater imaging and computation can help to study fine-scale dispersal and determine whether cryptic taxa are ecologically partitioned. Reduced representation sequencing can be conducted on wild populations and gives access to genomic variation across hundreds of individuals. Structure-from-motion photogrammetry enables the characterisation of structural features of the reef and coral colonies within reefs; thus, it is possible to combine high resolution spatial mapping and micro-environment analyses with genotyped colonies using these two technologies. 

Species of the Caribbean hard coral genus Agaricia (Order: Scleractinia) are arrayed over the entire depth range for photosynthetically dependent organisms, making them an ideal target for comparing mesophotic (>30 m depth) and shallow (<30 m) species, evaluating microhabitat differentiation, and assessing spatial structures across depths. My thesis uses this genus to explore questions related to spatial and environmental differentiation between and within taxa at scales from tens of kilometres to centimetres. The first data chapter (Chapter 2) of my thesis focuses on two mesophotic-occurring species: Agaricia grahamae and A. lamarcki. Despite presuming to be brooders with localised dispersal, no spatial population genetic structure was found over 10s of kms in either species. However, two sympatrically occurring cryptic taxa within each species were found. In A. lamarcki these taxa exhibited incomplete depth partitioning between shallow and mesophotic depths, yet taxa within A. grahamae displayed no obvious environmental distinctions. Demographic histories of all taxa were characterised by gene flow among taxa. This chapter exemplifies the complexities found in corals, where (1) spatial genetic structures do not follow expectations, (2) morphologically similar, sympatric taxa exist both at the same depths and differentiated by shallow and mesophotic depths and (3) gene flow among taxa may be important for the evolution of corals. My second and third data chapters (Chapters 3 and 4) focus on fine-scale characterisation of genotypes across 3D-imaged reefscapes within three depth zones (5, 10, 20 m) and among four sites along the leeward side of Curaçao and spread over ~50 km. Chapter 3 describes the delineation of cryptic coral taxa and investigates dispersal within and between depths among all taxa. The cryptic taxa are defined by divergent genotypic clusters occurring sympatrically and some were found to be associated with particular depth profiles. Disparate spatial genetic structures were found among congeners, where taxa within A. agaricites and A. humilis presented isolation-by-distance and dispersal distances across metres and, in contrast, A. lamarcki taxa presented genetic homogeneity at distances >50 km. This chapter provides one of the few estimates of dispersal distances in corals, which is exceedingly low (across metres), highlights the widespread cryptic diversity within corals and finds substantial differences in dispersal, clonality and genetic diversity among congeners. In Chapter 4, I used photogrammetry to characterise the microhabitat around individually genotyped colonies of Agaricia by deriving novel geometric measures. Environmental niches for sympatric cryptic taxa were determined by describing microhabitats that coral colonies inhabit. Species and cryptic taxa exhibited subtle divergences in their physical microhabitat niches. This chapter tackles the question of how cryptic coral taxa co-occur in seemingly similar environments and demonstrates a novel photogrammetric approach to characterise the microhabitat. 

My thesis applies new technologies and methods to help solve some of the mysteries of corals populations, namely, how far do larvae disperse? And what creates or preserves cryptic taxa? And in doing so, provides insight into coral ecology (interaction with microhabitat, spatial distribution, and dispersal) and evolution (cryptic diversification and hybridisation).

Abstract

Invasive alien species are among the main drivers of the ongoing sixth mass extinction wave, especially affecting island populations. Although the Caribbean is well-known for its high species richness and endemism, also for reptiles, equally important is the regional contribution of non-native species to island biodiversity. The Lesser Antilles encompass high genetic diversity in Iguana, though most native populations either have gone extinct or are declining following competitive hybridization with invasive non-native iguanas. Here we assessed non-native presence in two poorly-studied native melanistic Iguana iguana populations using available genetic tools, and explored utilizing size-dependent body measurements to discriminate between native and non-native iguanas. Genetic samples from Saba and Montserrat were genotyped across 17 microsatellite loci with STRUCTURE and multivariate analyses indicating non-native iguanas presence only on Saba. This was corroborated by mtDNA and nDNA sequences, highlighting a non-native origin in Central America and the ABC islands. We identied preliminary evidence suggestive of hybridization. Morphological variation among size-dependent characteristics showed that non-native iguanas have signicantly larger subtympanic plates than native iguanas. Non-native individuals also differed in scalation and coloration patterns. Overall, our ndings demonstrate the need for continuous monitoring for non-native iguanas within remaining native Iguana populations in the Lesser Antilles, with those not directly threatened by non-native iguanas restricted to only 8.7% of the historic range. Although genetic data allows for identication of non-native or hybrid iguana presence, this eld-to-lab workow is time consuming. Rapid in-situ identication of non-native individuals is crucial for conservation management, and besides scale and coloration patterns, we have highlighted the utility of size-dependent variables for rapid diagnosis. We urge regional partners to build morphometric databases for native Iguana populations that will help to quickly detect future incursions of non-native iguanas and allow the rapid implementation of effective countermeasures during the early phase of invasion.

Abstract

The Invasive Alien Green Iguana (IAGI), Iguana iguana, has spread worldwide via the pet trade, as stowaways and via other means and has become a pest species of global concern. It also represents a major threat to the endemic Lesser Antillean Iguana, Iguana delicatissima, on St. Eustatius. Following the capture of an adult female IAGI on St. Eustatius in early 2016, we conducted a Rapid Response Removal Campaign (RC) from April 2016 to January 2017. Three sets of directed visual surveys totaling 409.5 observer hours and covering a combined trajectory of 114.2 km realized only a single detection of a hybrid that was later removed. During the remainder of the campaign period, an additional four IAGI hybrids were opportunistically detected and removed thanks to park staff or community involvement. Since the end of the campaign, eight additional detections and removals have been realized, three of which were IAGIs caught while offloading freight in the harbour and five of which were hybrids caught in surrounding suburban areas. We suggest that at least four distinct IAGI introductions to St. Eustatius occurred between 2013 and 2020. Our results show the value of motivating and mobilizing stakeholders and the public at an early stage of an invasion. Since the program’s initiation, eight of the 13 iguanas detected for culling were thanks to public and key stakeholder support and involvement. Four years after our campaign, the number of IAGIs and their hybrids still appear to be limited and concentrated in and around inhabited areas. Additional removal campaigns should be initiated as soon as possible, firmly based in public outreach, motivation and engagement. New legislation is needed to prohibit the importation, possession and harbouring of IAGIs or hybrids and to provide a framework for long-term structural funding required for effective control and removal. Routine fumigation and rigorous inspection of arriving cargo to eliminate the risk of stowaway IAGIs are also recommended. Culling of IAGIs is recommended for the port of St. Maarten, which serves as a major point of dispersal of IAGIs to St. Eustatius and likely also other islands in the region.