Dataset Information

Progressive colonization and restricted gene flow shape island-dependent population structure in Galapagos marine iguanas (Amblyrhynchus cristatus).

ABSTRACT: BACKGROUND:Marine iguanas (Amblyrhynchus cristatus) inhabit the coastlines of large and small islands throughout the Galápagos archipelago, providing a rich system to study the spatial and temporal factors influencing the phylogeographic distribution and population structure of a species. Here, we analyze the microevolution of marine iguanas using the complete mitochondrial control region (CR) as well as 13 microsatellite loci representing more than 1200 individuals from 13 islands. RESULTS:CR data show that marine iguanas occupy three general clades: one that is widely distributed across the northern archipelago, and likely spread from east to west by way of the South Equatorial current, a second that is found mostly on the older eastern and central islands, and a third that is limited to the younger northern and western islands. Generally, the CR haplotype distribution pattern supports the colonization of the archipelago from the older, eastern islands to the younger, western islands. However, there are also signatures of recurrent, historical gene flow between islands after population establishment. Bayesian cluster analysis of microsatellite genotypes indicates the existence of twenty distinct genetic clusters generally following a one-cluster-per-island pattern. However, two well-differentiated clusters were found on the easternmost island of San Cristóbal, while nine distinct and highly intermixed clusters were found on youngest, westernmost islands of Isabela and Fernandina. High mtDNA and microsatellite genetic diversity were observed for populations on Isabela and Fernandina that may be the result of a recent population expansion and founder events from multiple sources. CONCLUSIONS:While a past genetic study based on pure FST analysis suggested that marine iguana populations display high levels of nuclear (but not mitochondrial) gene flow due to male-biased dispersal, the results of our sex-biased dispersal tests and the finding of strong genetic differentiation between islands do not support this view. Therefore, our study is a nice example of how recently developed analytical tools such as Bayesian clustering analysis and DNA sequence-based demographic analyses can overcome potential biases introduced by simply relying on FST estimates from markers with different inheritance patterns.

SUBMITTER: Steinfartz S

PROVIDER: S-EPMC2807874 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Progressive colonization and restricted gene flow shape island-dependent population structure in Galápagos marine iguanas (Amblyrhynchus cristatus).

Steinfartz Sebastian S Glaberman Scott S Lanterbecq Deborah D Russello Michael A MA Rosa Sabrina S Hanley Torrance C TC Marquez Cruz C Snell Howard L HL Snell Heidi M HM Gentile Gabriele G Dell'Olmo Giacomo G Powell Alessandro M AM Caccone Adalgisa A

BMC evolutionary biology 20091222

<h4>Background</h4>Marine iguanas (Amblyrhynchus cristatus) inhabit the coastlines of large and small islands throughout the Galápagos archipelago, providing a rich system to study the spatial and temporal factors influencing the phylogeographic distribution and population structure of a species. Here, we analyze the microevolution of marine iguanas using the complete mitochondrial control region (CR) as well as 13 microsatellite loci representing more than 1200 individuals from 13 islands.<h4>R ...[more]

PMID: 20028547

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Project description:The El Niño-Southern Oscillation (ENSO) is a major source of climatic disturbance, impacting the dynamics of ecosystems worldwide. Recent models predict that human-generated rises in green-house gas levels will cause an increase in the strength and frequency of El Niño warming events in the next several decades, highlighting the need to understand the potential biological consequences of increased ENSO activity. Studies have focused on the ecological and demographic implications of El Niño in a range of organisms, but there have been few systematic attempts to measure the impact of these processes on genetic diversity in populations. Here, we evaluate whether the 1997-1998 El Niño altered the genetic composition of Galápagos marine iguana populations from eleven islands, some of which experienced mortality rates of up to 90% as a result of El Niño warming. Specifically, we measured the temporal variation in microsatellite allele frequencies and mitochondrial DNA diversity (mtDNA) in samples collected before (1991/1993) and after (2004) the El Niño event. Based on microsatellite data, only one island (Marchena) showed signatures of a genetic bottleneck, where the harmonic mean of the effective population size (N(e)) was estimated to be less than 50 individuals during the period between samplings. Substantial decreases in mtDNA variation between time points were observed in populations from just two islands (Marchena and Genovesa). Our results suggests that, for the majority of islands, a single, intense El Niño event did not reduce marine iguana populations to the point where substantial neutral genetic diversity was lost. In the case of Marchena, simultaneous changes to both nuclear and mitochondrial DNA variation may also be the result of a volcanic eruption on the island in 1991. Therefore, studies that seek to evaluate the genetic impact of El Niño must also consider the confounding or potentially synergistic effect of other environmental and biological forces shaping populations.

Project description:BackgroundUnderstanding the natural microbiome and resistome of wildlife from remote places is necessary to monitor the human footprint on the environment including antimicrobial use (AU). Marine iguanas are endemic species from the Galapagos Islands where they are highly affected by anthropogenic factors that can alter their microbiota as well as their abundance and diversity of antimicrobial-resistant genes (ARGs). Thus, this study aims to apply culture-independent approaches to characterize the marine iguana's gut metagenomic composition of samples collected from the uninhabited islands Rabida (n = 8) and Fernandina (Cabo Douglas, n = 30; Punta Espinoza, n = 30). Fresh feces from marine iguanas were analyzed through SmartChip RT-PCR, 16S rRNA, and metagenomic next-generation sequencing (mNGS) to identify their microbiome, microbial-metabolic pathways, resistome, mobilome, and virulome.ResultsThe marine iguana's gut microbiome composition was highly conserved despite differences in ecological niches, where 86% of taxa were shared in the three locations. However, site-specific differences were mainly identified in resistome, mobilome, virulorome, and metabolic pathway composition, highlighting the existence of factors that induce microbial adaptations in each location. Functional gut microbiome analyses revealed its role in the biosynthesis and degradation of vitamins, cofactors, proteinogenic amino acids, carbohydrates, nucleosides and nucleotides, fatty acids, lipids, and other compounds necessary for the marine iguanas. The overall bacterial ARG abundance was relatively low (0.006%); nevertheless, the presence of genes encoding resistance to 22 drug classes was identified in the iguana's gut metagenome. ARG-carrying contig and co-occurrence network analyses revealed that commensal bacteria are the main hosts of ARGs. Taxa of public health interest such as Salmonella, Vibrio, and Klebsiella also carried multidrug-resistance genes associated with MGEs which can influence the dissemination of ARGs through horizontal gene transfer.ConclusionMarine iguanas depend on the gut microbiome for the biosynthesis and degradation of several compounds through a symbiotic relationship. Niche-specific adaptations were evidenced in the pool of microbial accessory genes (i.e., ARGs, MGEs, and virulence) and metabolic pathways, but not in the microbiome composition. Culture-independent approaches outlined the presence of a diverse resistome composition in the Galapagos marine iguanas from remote islands. The presence of AR pathogens in marine iguanas raises concerns about the dispersion of microbial-resistant threats in pristine areas, highlighting wildlife as sentinel species to identify the impact of AU.

Project description:BackgroundChemical signals are widely used in the animal kingdom, enabling communication in various social contexts, including mate selection and the establishment of dominance. Femoral glands, which produce and release waxy secretions into the environment, are organs of central importance in lizard chemical communication. The Galápagos marine iguana (Amblyrhynchus cristatus) is a squamate reptile with a lek-mating system. Although the lekking behaviour of marine iguanas has been well-studied, their potential for sexual communication via chemical cues has not yet been investigated. Here we describe the diversity of the lipophilic fraction of males' femoral gland secretions among 11 island populations of marine iguanas, and compare it with the composition of its sister species, the Galápagos land iguana (Conolophus subcristatus). We also conducted behavioural observations in marine iguana territorial males in order to explore the possible function of these substances in the context of male dominance in leks.MethodsFemoral secretions were analysed by gas chromatography coupled to mass spectrometry (GC-MS), and chromatography with a flame ionisation detector (GC-FID) in order to characterise the lipophilic composition. To understand the potential role of femoral secretions in marine iguana intraspecific communication, territorial males were sampled for their femoral glands and monitored to record their head bob rate-a territorial display behaviour in males-as well as the number of females present in their leks.ResultsWe found that the gland secretions were composed of ten saturated and unsaturated carboxylic acids ranging in chain length between C16 and C24, as well as three sterols. Cholesterol was the main compound found. Intriguingly, land iguanas have a higher diversity of lipophilic compounds, with structural group of lipids (i.e. aldehydes) entirely absent in marine iguanas; overall the chemical signals of both species were strongly differentiated. Lipid profiles also differed among populations of marine iguanas from different islands, with some islands demonstrating a high diversity of lipophilic compounds (i.e. full spectra of compounds), and others lacking one or more compounds. Among the compounds most frequently found missing were 11- and 13-eicosenoic acids. Gland secretions of males with a better body condition and with a higher dominance status (i.e. those accompanied by females and with higher head bob display) were proportionately richer in C20-unsaturated fatty acids (11-eicosenoic acid).DiscussionLand and marine iguanas strongly diverged in their chemical composition of the femoral glands likely due to ecological differences between both species. Despite that marine iguana populations varied in their femoral gland composition that was not related to their genetic structure. Our results indicated that 11-eicosenoic acid may play an important role in intraspecific chemical communication in marine iguanas.

Dataset Information

Progressive colonization and restricted gene flow shape island-dependent population structure in Galapagos marine iguanas (Amblyrhynchus cristatus).

Publications

Progressive colonization and restricted gene flow shape island-dependent population structure in Galápagos marine iguanas (Amblyrhynchus cristatus).

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