Marine Iguanas Research Articles

Galapagos Islands Endemic Vertebrates: A Population Genetics Perspective.

The organisms of the Galapagos Islands played a central role in the development of the theory of evolution by Charles Darwin. Examination of the population genetics factors of many of these organisms with modern molecular methods has expanded our understanding of their evolution. Here, I provide a perspective on how selection, gene flow, genetic drift, mutation, and inbreeding have contributed to the evolution of 6 iconic Galapagos species: flightless cormorant, pink iguana, marine iguana, Galapagos hawk, giant tortoises, and Darwin's finches. Because of the inherent biological differences among these species that have colonized the Galapagos, different population genetic factors appear to be more or less important in these different species. For example, the Galapagos provided novel environments in which strong selection took place and the Darwin's finches diversified to produce new species and the cormorant adapted to the nutrient-rich western shores of the Galapagos by losing its ability to fly and genomic data have now identified candidate genes. In both the pink iguana, which exists in one small population, and the Galapagos hawk, which has small population sizes, genetic drift has been potentially quite important. There appears to be very limited interisland gene flow in the flightless cormorant and the Galapagos hawk. On the other hand, both the marine iguana and some of the Darwin's finches appear to have significant interisland gene flow. Hybridization between species and subspecies has also introduced new adaptive variation, and in some cases, hybridization might have resulted in despeciation. Overall, new population genetics and genomics research has provided additional insight into the evolution of vertebrate species in the Galapagos.

Emergence/Subsidence Histories Along the Carnegie and Cocos Ridges and Their Bearing Upon Biological Speciation in the Galápagos

AbstractUsing plate motion reconstructions for the Nazca, Cocos, and South American plates in relation to the Galápagos hotspot, we find that age‐depth dependence of bathymetry, Galápagos plume dynamic topography, crustal relaxation, and magmatic production permit reasonable estimates for the subsidence of former islands along the Carnegie and Cocos Ridges. Our dynamic topography estimates are partially based upon geodynamic theory (fluid mechanics and elasticity) and also upon detailed bathymetric observations and analysis. For three different target areas over Carnegie Ridge and two over Cocos Ridge, we infer subaerial landmasses over the past ~20 Ma. We provide rough estimates of the surface areas of these paleo‐archipelagos, which were comparable to that of the present‐day Galápagos archipelago. We construct a history of emerged (paleo‐island) topography along the conjugate pair Carnegie‐Cocos hotspot tracks and infer that significant subaerial landscapes existed for at least the past ~20 Ma. The genetic ancestors of endemic faunal species in Galápagos (e.g., marine iguanas) migrated away from South America, genetically diverging from their land counterparts much earlier than the age of the present Galápagos Islands (~3 Ma). At 16.5 Ma, the total emerged landmass on the Carnegie Ridge alone may have been ~2.5 times that of the current Galápagos archipelago. (The conjugate landmass along the Cocos Ridge has been subducted.) We propose that this large landmass, at least one‐fourth the size of Iceland, be called Darwinia in recognition of its importance in the evolution of some Galápagos endemic flora and fauna made famous by Darwin's explorations.

Field-Based Radiographic Imaging of Marine Megafauna: Marine Iguanas (Amblyrhynchus cristatus) as a Case Study

Effective conservation of marine megafauna requires a thorough understanding of the ecology, physiology, population dynamics, and health of vulnerable species. Assessing the health of large, mobile marine animals poses particular challenges, in part because the subjects are difficult to capture and restrain, and in part because standard laboratory and diagnostic tools are difficult to apply in a field setting. Radiography is a critically important diagnostic tool used routinely by veterinarians, but it has seldom been possible to image live marine vertebrates in the field. As a first step toward assessing the feasibility of incorporating radiography into studies of vulnerable species in remote locations, we used portable radiographic equipment to acquire the first digital internal images of living marine iguanas, Amblyrhynchus cristatus, an iconic lizard endemic only to the Galapagos Islands of Ecuador. The radiographic machinery was powered by batteries and performed well on a rocky beach environment of an uninhabited island, despite high heat and humidity. The accuracy of radiographic measurements was validated by computing a snout-vent length (SVL) using bone dimensions and comparing this to standard measurements of SVL made externally with a tape measure. These results demonstrate the feasibility of using radiography to study animals in remote sites, a technique that may prove useful for a variety of physiological, ecological, and biomechanical studies in which reliable measurements of skeletal and soft-tissue dimensions must be acquired under challenging field conditions. Refinements are discussed that will help the technology reach its full potential in field studies.

Characterization of lipid structures in femoral secretions of Galápagos marine iguanas by shotgun lipidomics

The lipidome of femoral gland secretions of the marine iguana (Amblyrhynchus cristatus) was studied. The main aim of this work was to identify and quantify the lipids present in femoral secretions using mass spectrometry-based shotgun lipidomics. Lipids belonging to seven lipid classes were identified: ceramides (43.41%), triacylglycerols (42.15%), cholesteryl esters (4.18%), sphingomyelins (3.61%), phosphatidylcholines (2.67%), phosphatidylinositols (2.50%) and phosphatidylethanolamines (1.48%). The second aim of the study was to explore whether lipid composition matches the different subspecies or populations of marine iguanas. The different subspecies of iguanas did not group together in relation to their lipidome. The authors’ findings are discussed in an ecological context and compared with the results of a previous study that characterized volatile lipids in marine iguana secretions using gas chromatography. Given the high diversity of lipid structures in femoral secretions discovered in this study, it is likely that some of these could be involved in intraspecific communication. Certain lipids could have other functions, such as building a barrier to avoid water loss. More data needs to be added to explore this hypothesis. This study is the first to use a lipidomics-based approach to characterize lipid composition in lizard femoral secretions. The application of shotgun lipidomics to reptilian glandular secretions will shed new light on the potential function of lipids in intraspecific chemical communication.

Diversity of compounds in femoral secretions of Galápagos iguanas (genera: Amblyrhynchus and Conolophus), and their potential role in sexual communication in lek-mating marine iguanas (Amblyrhynchus cristatus).

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.

Shedding light on the Imps of Darkness: an integrative taxonomic revision of the Galápagos marine iguanas (genus Amblyrhynchus)

Shedding light on the Imps of Darkness: an integrative taxonomic revision of the Galápagos marine iguanas (genus Amblyrhynchus)

Too much of a good thing? Human disturbance linked to ecotourism has a “dose-dependent” impact on innate immunity and oxidative stress in marine iguanas, Amblyrhynchus cristatus

Human population and thus anthropogenic disturbance of natural systems are increasing at staggering rates. However, the impact of disturbance on natural systems likely varies with the extent of disturbance. While a considerable amount of research has been conducted on high-impact disturbances (e.g., environmental contamination, urban development), much less is known about the effects of less obtrusive activities such as ecotourism and outdoor recreation. Past research has documented behavioral and hormonal changes to non-consumptive wildlife activities; however, these studies rarely provide direct health and survival consequences, or examine impacts over a gradient of disturbances. In the current study, we quantified endocrine and immune responses and reproductive investment in six Galápagos marine iguana (Amblyrhynchus cristatus) populations located across a gradient of human disturbance stemming from the ecotourism industry, including urban development, boat traffic, and ecotourist activities. We regressed fitness-related physiological metrics to the intensity of human disturbance across these populations. As predicted, immunological capabilities decreased and oxidative stress increased with increasing intensity of human disturbance and development. Sexes also differed in their endocrine responses to disturbance intensity, with only males showing elevated baseline corticosterone at sites impacted by tourism. Testosterone and estradiol were both positively related to disturbance intensity. There was also a significant overall negative effect of the presence of human disturbance, but not its intensity, on reproductive investment. These results are the first to demonstrate that measures of physiological performance are sensitive to the intensity, and not merely the presence/absence of human disturbance, and that immunological measures in addition to more traditional methods can serve as important indicators of stress and potentially compromised fitness in natural populations.

Lessons of the Galapagos

Hiking slowly over the rocky terrain, I tune into the whistling and honking sounds around me, being careful not to step on the radiating blue feet that are literally in my path. A colony of blue-footed boobies intent on the business of courtship dances and displays surrounds me. Just when I think it can't get any better, a male, red-flanked marine iguana gently steps over my boot as he makes his way toward the water's edge to feed on algae. This was my experience on my first visit to the Galapagos Islands. I was awestruck by the uniqueness of these enchanted isles and the natural lessons they present. A biology teacher and naturalist at heart, I have an affinity for wild places and for birding, photographing plants and animals, and learning about species and their natural history. In my classroom, nature serves as a tool to connect students to relevant biological concepts and processes through anecdotes, discussion, multimedia, and studying alluring species. Many endemic species of the Galapagos are captivating and useful for a biology teacher planning an extended lesson on evolution. To promote teaching science through inquiry, I wanted to use my experience in the Galapagos to design a lesson that allows students to immerse themselves in the essential science and engineering practices identified in the Next Generation Science Standards (NGSS Lead States 2013; see box, p. 46), as they ask questions; analyze and interpret data; engage in argument from evidence; and obtain, evaluate, and communicate information. Students may have preconceived ideas and sometimes misconceptions about evolution from their previous experiences, so a lesson plan must reflect the contemporary constructionist view of learning wherein students redefine, reorganize, expand, and change their initial concepts and views through classroom activities and experiences while interacting with other students and their environment. To satisfy these concerns, I followed the 5E instructional model (Trowbridge, Bybee, and Powell 2000). This model describes a sequence of phases--engagement, exploration, explanation, elaboration, and evaluation--that align with both inquiry processes and constructivism. Engaging islands During the engagement phase, the challenge is to gain students' attention, spark their inquisitiveness, and have them pose initial questions. Showing an enticing video clip, passing around photographs, projecting a slide show of an attractive species such as the Galapagos hawk (Buteo galapagoensis), or describing a spectacle such as that of the male great frigatebird (Fregata minor ridgwayi) in his courtship ritual work for me as a way to accomplish this task. I then have students pose their own questions about the features, location, wildlife, and scientific significance of the islands to assess their prior knowledge. This discussion generates some useful Galapagos facts, and presenting a brief history and description of Darwin's Islands further serves to establish a base of knowledge. Once students have been engaged, they can be given--or research for themselves--some geographical information about the island. These oceanic islands form an archipelago that consists of 13 relatively large islands, each with an area greater than 10 km2, six smaller islands, and more than 40 named islets. Formed from undersea volcanoes three million to five million years ago, the islands today straddle the equator some 960 km from the coast of Ecuador on the South American mainland (Jackson 2001). Because these islands sit in the middle of nowhere, so to speak, the question arises as to how plants and animals colonized and inhabited them, especially in view of the geologic fact that these volcanic islands were barren when they first appeared above the sea's surface. At this point, student exchanges and discussion focus attention on dispersal mechanisms and island colonization. By the end of this introduction, the class acquires insights into possible dispersal mechanisms to the Galapagos from potential mainland areas: for example, by sea for penguins and marine mammals; through floating vegetation rafts for insects and reptiles; by air for seabirds; and by wind for plants, lichens, and fungi. …

Endocrine-reproductive-immune interactions in female and male Galápagos marine iguanas

Endocrine-immune interactions are variable across species and contexts making it difficult to discern consistent patterns. There is a paucity of data in non-model systems making these relationships even more nebulous, particularly in reptiles. In the present study, we have completed a more comprehensive test of the relationship among steroid hormones and ecologically relevant immune measures. We tested the relationship between baseline and stress-induced levels of sex and adrenal steroid hormones and standard ecoimmunological metrics in both female and male Galápagos marine iguanas (Amblyrhynchus cristatus). We found significant associations between adrenal activity and immunity, whereby females that mounted greater corticosterone responses to stress had lower basal and stress-induced immunity (i.e., bactericidal ability). Males showed the opposite relationship, suggesting sex-specific immunomodulatory actions of corticosterone. In both sexes, we observed a stress-induced increase in corticosterone, and in females a stress-induced increase in bactericidal ability. Consistent with other taxa, we also found that baseline corticosterone and testosterone in males was inversely related to baseline bactericidal ability. However, in females, we found a positive relationship between both testosterone and progesterone and bactericidal ability. Multivariate analysis did not discern any further endocrine-immune relationships, suggesting that interactions between adrenal, sex steroid hormones, and the immune system may not be direct and instead may be responding to other common stimuli, (i.e., reproductive status, energy). Taken together, these data illustrate significant endocrine-immune interactions that are highly dependent on sex and the stress state of the animal.

Galápagos macroalgae: A review of the state of ecological knowledge.

Previous work has highlighted the critical role of macroalgal productivity and dynamics in supporting and structuring marine food webs. Spatio-temporal variability in macroalgae can alter coastal ecosystems, a relationship particularly visible along upwelling-influenced coastlines. As a result of its equatorial location and nutrient rich, upwelling-influenced waters, the Galápagos Archipelago in the East Pacific, hosts a productive and biodiverse marine ecosystem. Reports and collections of macroalgae date back to the Beagle voyage, and since then, more than three hundred species have been reported. However, their ecology and functional role in the ecosystem is not well understood. According to various disparate and in part anecdotal sources of information, abundant and diverse communities exist in the Western regions of the archipelago, the North is essentially barren, and in the central/South abundance and distribution is variable and less well defined. Both oceanographic conditions and herbivore influence have been theorized to cause this pattern. Extensive changes in macroalgal productivity and community composition have occurred during strong ENSO events, and subsequent declines in marine iguana (an endemic and iconic grazer) populations have been linked to these changes. Iguanas are only one species of a diverse and abundant group of marine grazers in the system, highlighting the potentially important role of macroalgal productivity in the marine food web. This review represents a first compilation and discussion of the available literature and presents topics for future research.

Ecological and evolutionary influences on body size and shape in the Galápagos marine iguana (Amblyrhynchus cristatus).

Oceanic islands are often inhabited by endemic species that have undergone substantial morphological evolutionary change due to processes of multiple colonizations from various source populations, dispersal, and local adaptation. Galápagos marine iguanas are an example of an island endemic exhibiting high morphological diversity, including substantial body size variation among populations and sexes, but the causes and magnitude of this variation are not well understood. We obtained morphological measurements from marine iguanas throughout their distribution range. These data were combined with genetic and local environmental data from each population to investigate the effects of evolutionary history and environmental conditions on body size and shape variation and sexual dimorphism. Our results indicate that body size and shape are highly variable among populations. Sea surface temperature and island perimeter, but not evolutionary history as depicted by phylogeographic patterns in this species, explain variation in body size among populations. Conversely, evolutionary history, but not environmental parameters or island size, was found to influence variation in body shape among populations. Finally, in all populations except one, we found strong sexual dimorphism in body size and shape in which males are larger, with higher heads than females, while females have longer heads than males. Differences among populations suggest that plasticity and/or genetic adaptation may shape body size and shape variation in marine iguanas. This study will help target future investigations to address the contribution of plasticity versus genetic adaptation on size and shape variation in marine iguanas.

The conservation status of the Galápagos marine iguanas, Amblyrhynchus cristatus: a molecular perspective

Traditionally, conservation management focuses efforts on taxonomic units. However, when the taxa used do not reflect biologically meaningful units, such methods should be reconsidered to avoid the loss of irreplaceable biodiversity. The Galápagos marine iguana (Amblyrhynchus cristatus) is listed as Vulnerable on the IUCN Red List of Threatened Species and is facing growing anthropogenic threats. Currently, management is based on a taxonomy which is questionable in the light of recent molecular data. As such, there is a danger that evolutionarily significant populations may be left vulnerable to extirpation. Herein, we apply molecular data to elucidate the population structure of this species across the Galápagos archipelago, and thus advise conservation management in the absence of a revised taxonomy. Applying a wealth of molecular data including 12 microsatellite loci and 1181 bp of the mitochondrial control region in over 1200 individuals, we delineate distinct populations and prioritize their management. Bayesian population structure analysis revealed 10 distinct population clusters, which we propose as management units (MUs). All MUs are significantly differentiated, with one unit on San Cristóbal Island being particularly distinct in terms of both microsatellite loci and mitochondrial data. Based on estimates of the genetic effective population size (Ne), we find the MUs comprised of populations occurring on Floreana, Española, Marchena, and San Cristóbal to be alarmingly small. In consideration of both Neand anthropogenic threats, we recommend that conservation practitioners focus efforts on Floreana and San Cristóbal islands, and argue that better census size estimates of populations are urgently needed.

The complete mitochondrial genomes of the Galápagos iguanas, Amblyrhynchus cristatus and Conolophus subcristatus

The Galápagos iguanas are among the oldest vertebrate lineages on the Galápagos archipelago, and the evolutionary history of this clade is of great interest to biologists. We describe here the complete mitochondrial genomes of the marine iguana, Amblyrhynchus cristatus (Genbank accession number: KT277937) and the land iguana Conolophus subcristatus (Genbank accession number: KT277936). The genomes contain 13 protein-coding genes, 22 transfer RNAs, and two ribosomal RNAs genes, as well as a control region (CR). Both species have an identical gene order, which matches that of Iguana iguana. The CR of both Galápagos iguanas features similar tandem repeats units, which are absent in I. iguana. We present a phylogeny of the Iguanidae based on complete mitochondrial genomes, which confirms the sister-group relationship of Galápagos iguanas. These new mitochondrial genomes constitute an important data source for future exploration of the phylogenetic relationships and evolutionary history of the Galápagos iguanas.

Environmental constraints on haul-out and foraging dynamics in Galápagos marine iguanas

Environmental constraints on haul-out and foraging dynamics in Galápagos marine iguanas

Hybridization masks speciation in the evolutionary history of the Galápagos marine iguana.

The effects of the direct interaction between hybridization and speciation-two major contrasting evolutionary processes--are poorly understood. We present here the evolutionary history of the Galápagos marine iguana (Amblyrhynchus cristatus) and reveal a case of incipient within--island speciation, which is paralleled by between-island hybridization. In-depth genome-wide analyses suggest that Amblyrhynchus diverged from its sister group, the Galápagos land iguanas, around 4.5 million years ago (Ma), but divergence among extant populations is exceedingly young (less than 50,000 years). Despite Amblyrhynchus appearing as a single long-branch species phylogenetically, we find strong population structure between islands, and one case of incipient speciation of sister lineages within the same island--ostensibly initiated by volcanic events. Hybridization between both lineages is exceedingly rare, yet frequent hybridization with migrants from nearby islands is evident. The contemporary snapshot provided by highly variable markers indicates that speciation events may have occurred throughout the evolutionary history of marine iguanas, though these events are not visible in the deeper phylogenetic trees. We hypothesize that the observed interplay of speciation and hybridization might be a mechanism by which local adaptations, generated by incipient speciation, can be absorbed into a common gene pool, thereby enhancing the evolutionary potential of the species as a whole.

Long bone histology and microanatomy of Placodontia (Diapsida: Sauropterygia)

Placodontia, an enigmatic group of durophagous and in part heavily armoured animals, were members of Sauropterygia, the most diverse and successful group of Mesozoic marine reptiles. Microanatomy and histology of long bones of several armoured and non-armoured Placodontia were studied, covering most of their taxonomic breadth, to elucidate the paleoecology, physiology, and lifestyle of its members. Results reveal an unexpected and not phylogenetically or stratigraphically related disparity of microanatomical and histological features for the group. The non-armoured Paraplacodus and the heavily armoured Psephoderma grew with lamellar-zonal bone tissue type, which is typical for modern sauropsids. In the former, the tissue is nearly avascular surrounding a compacted medullary region, whereas in the latter, the lamellar-zonal bone tissue is vascularized framing a large open medullary cavity and a perimedullary region. Armoured Henodus and Placodontia indet. aff. Cyamodus as well as non-armoured Placodus exhibit a reduced medullary cavity and grew with highly vascularized plexiform to radiating fibro-lamellar bone. Several long bones of Placodontia indet. show circumferential fibro-lamellar bone and can be distinguished into two groups on the basis of microanatomical features. In addition, all bones that grew with fibro-lamellar bone show locally primary spongeous-like architecture and had secondarily widened primary osteons throughout the cortex, resulting in a secondarily spongeous tissue. The highly vascularized fibro-lamellar bone of these Placodontia indicates growth rates comparable to that of open marine ichthyosaurs. Differences in microanatomy and bone histology as expressed by a principal component analysis, thus clearly indicate different paleoecologies, including differences in lifestyle and swimming modes and capabilities in Placodontia. This would have reduced competition in the shallow marine environments of the Tethys and might be a key to their success and diversity. A certain developmental plasticity among the studied placodonts is interpreted as response to different environmental conditions as is obvious from inter- and intraspecific histological variation. Most striking is the difference in life history strategy in armoured Psephoderma and non-armoured Paraplacodus when compared to armoured Henodus, Placodontia indet. aff. Cyamodus, non-armoured Placodus, and Placodontia indet. Bone tissue of Psephoderma and Paraplacodus indicates low growth rates and a low basal metabolic rate, as many modern sauropsids have such as the marine iguana, whereas the others grew with extremely fast growth rates, more typical for birds and mammals, indicating an increased basal metabolic rate.

Blood gases, biochemistry and haematology of Galápagos marine iguanas (Amblyrhynchus cristatus).

The marine iguana, Amblyrhynchus cristatus, is an iconic lizard endemic to the Galápagos Islands of Ecuador, but surprisingly little information exists on baseline health parameters for this species. We analysed blood samples drawn from 35 marine iguanas captured at three locations on San Cristóbal Island. A portable blood analyser (iSTAT) was used to obtain near-immediate field results for pH, lactate, partial pressure of O2, partial pressure of CO2, bicarbonate (HCO3 (-)), percentage O2 saturation, haematocrit, haemoglobin, sodium, potassium, ionized calcium and glucose. Parameter values affected by temperature were auto-corrected by the iSTAT. Standard laboratory haematology techniques were employed for differential white blood cell counts and haematocrit determination; resulting values were also compared with the haematocrit values generated by the iSTAT. Body temperature, heart rate, respiratory rate and body measurements were also recorded. Body length was positively correlated with several blood chemistry values (HCO3 (-) and glucose) and two haematology parameters (haemoglobin and manually determined haematocrit). A notable finding was the unusually high blood sodium level; the mean value of 178 mg/dl is among the highest known for any reptile. This value is likely to be a conservative estimate because some samples exceeded the maximal value the iSTAT can detect. For haematocrit determination, the iSTAT blood analyser yielded results significantly lower than those obtained with high-speed centrifugation. The values reported in this study provide baseline data that may be useful in comparisons among populations and in detecting changes in health status among marine iguanas affected by natural disturbances or anthropogenic threats. The findings might also be helpful in future efforts to demonstrate associations between specific biochemical parameters and disease.

Metagenomic-based study of the phylogenetic and functional gene diversity in Galápagos land and marine iguanas.

In this study, a metagenome-based analysis of the fecal samples from the macrophytic algae-consuming marine iguana (MI; Amblyrhynchus cristatus) and terrestrial biomass-consuming land iguanas (LI; Conolophus spp.) was conducted. Phylogenetic affiliations of the fecal microbiome were more similar between both iguanas than to other mammalian herbivorous hosts. However, functional gene diversities in both MI and LI iguana hosts differed in relation to the diet, where the MI fecal microbiota had a functional diversity that clustered apart from the other terrestrial-biomass consuming reptilian and mammalian hosts. A further examination of the carbohydrate-degrading genes revealed that several of the prevalent glycosyl hydrolases (GH), glycosyl transferases (GT), carbohydrate binding modules (CBM), and carbohydrate esterases (CE) gene classes were conserved among all examined herbivorous hosts, reiterating the important roles these genes play in the breakdown and metabolism of herbivorous diets. Genes encoding some classes of carbohydrate-degrading families, including GH2, GH13, GT2, GT4, CBM50, CBM48, CE4, and CE11, as well as genes associated with sulfur metabolism and dehalogenation, were highly enriched or unique to the MI. In contrast, gene sequences that relate to archaeal methanogenesis were detected only in LI fecal microbiome, and genes coding for GH13, GH66, GT2, GT4, CBM50, CBM13, CE4, and CE8 carbohydrate active enzymes were highly abundant in the LI. Bacterial populations were enriched on various carbohydrates substrates (e.g., glucose, arabinose, xylose). The majority of the enriched bacterial populations belong to genera Clostridium spp. and Enterococcus spp. that likely accounted for the high prevalence of GH13 and GH2, as well as the GT families (e.g., GT2, GT4, GT28, GT35, and GT51) that were ubiquitously present in the fecal microbiota of all herbivorous hosts.

Oceanographic and climatic variation drive top‐down/bottom‐up coupling in the Galápagos intertidal meta‐ecosystem

The impact of herbivores on primary producers in differing oceanographic regimes is a matter of intense ecological interest due to ongoing changes in their abundance, that of their predators, and anthropomorphic alteration of nutrient cycles and climatic patterns. Interactions between productivity and herbivory in marine habitats have been studied on temperate rocky shores, coral reefs, mangroves, and salt marshes, but less so at tropical latitudes. To determine how herbivore–alga dynamics varied with oceanographic regime, we used the comparative‐experimental approach in rocky intertidal communities on the Galápagos Islands from January 2006 to January 2009. This setting was selected because strongly contrasting oceanographic conditions occurred within a range of ∼181 km, with significant differences in temperature, nutrients, phytoplankton productivity, and intertidal communities, and in abundance of macro‐herbivores, including marine iguanas. Experiments and measurements were conducted at two sites in each of three oceanographic regimes characterized by low, intermediate, and high bottom‐up inputs. At sites of low inputs, macro‐herbivores (fish, crabs, iguanas) had a consistent top‐down effect, reducing algal abundance, and leaving a few grazer‐resistant varieties. At sites of intermediate and high inputs, consumer impacts were stronger during La Niña (cool phase) than during El Niño (warm phase). At sites of high inputs, algal biomass was naturally relatively high and was dominated by the edible algae Ulva spp. Macro‐grazers reduced algal biomass, but their primary effect was indirect, as articulated corallines displaced other species of algae in their absence. Prior results from the tropics had revealed dominant effects of top‐down interactions and recruitment in structuring intertidal communities. Our results suggest that, when a broader oceanographic scenario is taken into account, the relative importance of top‐down and bottom‐up forces are context dependent, varying with oceanographic regime and climatic variability.

The early scientific history of Galapagos iguanas

The oldest known specimen of Galapagos marine iguana (Amblyrhynchus cristatus), now in the University Museum, Oxford, was originally thought to have come from Mexico. A plausible history of its origin with sealers in the Galapagos Islands about 1824 and transportation to and across Mexico is advanced. The naturalists David Douglas and John Scouler, on James (Santiago) Island in January 1825, encountered and attempted unsuccessfully to preserve specimens of the land iguana (Conolophus subcristatus) but only a Scouler specimen of marine iguana made it back to England, and it has since disappeared. Published and previously unpublished journal entries from the voyage of HMS Blonde, which had shore parties at Albemarle (Isabela) and Narborough (Fernandina) islands in March 1825, establish that the specimens on which the original description of Amblyrhynchus (later Conolophus) subcristatus J. E. Gray, 1831 , was based originated in the voyage of the Blonde. Banks Bay, Albemarle Island, is here designated as the type locality for Conolophus subcristatus. Specimens of the marine iguana were also brought back by the Blonde. The published accounts of Scouler and the voyage of the Blonde established the Galapagos as the true home of the marine iguana well before the return of Charles Darwin and HMS Beagle in 1836.