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BACKGROUND: The Eastern Tropical Pacific (ETP) harbors a great diversity of Porifera. In particular, the Aplysina genus has acquired biotechnological and pharmacological importance. Nevertheless, the ecological aspects of their species and populations have been poorly studied. Aplysina gerardogreeni is the most conspicuous verongid sponge from the ETP, where it is usually found on rocky-coralline ecosystems. We evaluated the polymorphism levels of 18 microsatellites obtained from next-generation sequencing technologies. Furthermore, we tested the null hypothesis of panmixia in A. gerardogreeni population from two Mexican-Pacific localities. METHODS AND RESULTS: A total of 6,128,000 paired reads were processed of which primer sets of 18 microsatellites were designed. The loci were tested in 64 specimens from Mazatlan, Sinaloa (N = 32) and Isabel Island, Nayarit (N = 32). The microsatellites developed were moderately polymorphic with a range of alleles between 2 and 11, and Ho between 0.069 and 0.785. Fifteen loci displayed significant deviation from the Hardy-Weinberg equilibrium. No linkage disequilibrium was detected. A strong genetic structure was confirmed between localities using hierarchical Bayesian analyses, principal coordinates analyses, and fixation indices (FST = 0.108*). All the samples were assigned to their locality; however, there was a small sign of mixing between localities. CONCLUSIONS: Despite the moderate values of diversity in microsatellites, they showed a strong signal of genetic structure between populations. We suggest that these molecular markers can be a relevant tool to evaluate all populations across the ETP. In addition, 17 of these microsatellites were successfully amplified in the species A. fistularis and A. lacunosa, meaning they could also be applied in congeneric sponges from the Caribbean Sea. The use of these molecular markers in population genetic studies will allow assessment of the connectivity patterns in species of the Aplysina genus.

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BACKGROUND: Mycale cecilia is an abundant Eastern Tropical Pacific sponge living in a wide variety of habitats, including coral reefs where it may directly interact with corals. It is also known to possess secondary metabolites of pharmacological value. These aspects highlight the importance of having a better understanding of its biology, and genetic and population diversity. METHODS AND RESULTS: In the present study, we isolated and characterized twelve novel microsatellite loci by Illumina MiSeq sequencing. The loci were tested in 30 specimens collected from two coral reef localities (La Paz, Baja California Sur and Isabel Island, Nayarit) from the Mexican Pacific using M13(-21) labeling. All loci were polymorphic, with two to nine alleles per locus. Expected heterozygosities varied from 0.616 to 0.901. Eleven loci were tested and successfully amplified in M. microsigmatosa from the Gulf of Mexico. CONCLUSION: Here we report the first microsatellite loci developed for a sponge species from the Eastern Pacific coast. These molecular markers will be used for population genetic studies of M. cecilia, and potentially in other congeneric species; particularly in vulnerable marine areas that require protection, such as coral reefs.

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Withering syndrome (WS) is a gastro-intestinal (GI) infectious disease likely affecting all abalone species worldwide. Structural and functional changes in abalone GI microbiotas under WS-stressed conditions remain poorly investigated. It is unclear if interspecific microbiota differences, such as the presence of certain microbes, their abundance, and functional capabilities, may be involved in the occurrence of this disease. Bacterial microbiotas of healthy Haliotis fulgens and Haliotis corrugata are mainly composed by Tenericutes, Proteobacteria, Fusobacteria, and Spirochaetes. We previously reported species-specific structural and functional profiles of those communities and suggested that they are of consequence to the different susceptibility of each species to WS. Here, we address this question by comparing the structure and function of healthy and dysbiotic microbiota through 454 pyrosequencing and PICRUSt 2, respectively. Our findings suggest that the extent to which WS-stressed conditions may explain structural and functional differences in GI microbiota is contingent on the microbiota diversity itself. Indeed, microbiota differences between stressed and healthy abalone were marginal in the more complex bacterial communities of H. corrugata, in which no significant structural or functional changes were detected. Conversely, significant structural changes were observed in the less complex bacterial microbiota of H. fulgens. Moreover, structural alterations led to a significant downregulation of some metabolic activities conducted by GI bacteria. Accordingly, results suggest that gastro-intestinal bacterial diversity appears to be related with both the health of abalone and the etiology of WS.

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The complete mitogenome of Thoosa mismalolli Carballo, Cruz-Barraza & Gómez, 2004 (Tetractinellida, Thoosidae) was sequenced. This is the first complete mitogenome of the suborden Thoosina and the third Tetractinellid so far. The mitochondrial genome of T. mismalolli was assembled based on reads obtained with the Illumina HiSeq platform. The length of complete mitogenome is 19,019 bp long and contained 14 protein-coding genes and 23 tRNA, with two tRNA genes. Phylogenetic reconstruction (maximum-likelihood) based on mitogenome of Tetractinellids, supports T. mismalolli as a sister group. This result is congruent with those obtained with molecular markers (CO1, 18S, and 28S), supporting the monophyletic status of Thoosa and providing additional molecular data in favor of the suborder Thoosina.

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Kinorhyncha is a phylum of exclusively marine, meiofaunal invertebrates (Sørensen Pardos 2008). Currently, the knowledge about the worldwide distribution of most of its species is considerably patchy, as several taxa have been reported from a single or few localities, usually within a limited geographic area (Sørensen Pardos 2008; Yamasaki et al. 2018a). This even becomes more evident for deep-sea kinorhynchs, as noticed by Sørensen et al. (2018). Given the particular value of new records from the deep-sea to increase our understanding in the distribution of meiofaunal organisms plus the observed relationship of morphological variation through the bathymetric gradient, we aim to report the first record of Echinoderes unispinosus Yamasaki, Neuhaus George, 2018 in the southern edge of the Gulf of Mexico (GoM), and contribute with new information about the morphological intraspecific variation of this species. In Mexico, studies of kinorhynch biodiversity are limited to the northern Gulf of California (50-1570m depth) (Álvarez-Castillo et al. 2015, 2018; Cepeda et al. 2019) and the Yucatán Peninsula (Sánchez Martínez 2019). The GoM is a semi-closed basin located in a transition zone with both subtropical and tropical weather. Deep-sea muddy sediment samples of the present study were collected during the expedition XIXIMI-5 (10-24 June 2016) and processed according to Cisterna-Céliz et al. (2019). Kinorhynch specimens were mounted, measured and photographed according to Cepeda et al. (2019). Two adult males were identified as E. unispinosus, one from station B11 (2298 m depth) and another from station B15 (3708m depth). Kinorhynch specimens were deposited at the Aquatic Invertebrates Collection of the Facultad de Ciencias, Universidad Nacional Autónoma de México (UNAM), Mexico, under accession numbers: KGM.001 and KGM.002.

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We report the first mitochondrial genome of a Verongid sponge, Aplysina gerardogreeni from the Pacific Ocean. This has 19,620 bp and includes 14 protein-coding genes, 2 rRNAs genes, and 25 tRNAs genes. The gene arrangement was similar to the one found in two Caribbean Aplysina mitogenomes previously reported. Comparative analyses revealed a few substitutions among congeneric mitogenomes. The mitogenome of A. gerardogreeni could be useful to study the evolution of Verongimorpha group and also to identify adequate genes for its molecular systematics.

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The GI microbiota of abalone contains a highly complex bacterial assemblage playing an essential role in the overall health of these gastropods. The gut bacterial communities of abalone species characterized so far reveal considerable interspecific variability, likely resulting from bacterial interactions and constrained by the ecology of their abalone host species; however, they remain poorly investigated. Additionally, the extent to which structural changes in the microbiota entail functional shifts in metabolic pathways of bacterial communities remains unexplored. In order to address these questions, we characterized the gut microbiota of the northeast Pacific blue (Haliotis fulgens or HF) and yellow (Haliotis corrugata or HC) abalone by 16S rRNA gene pyrosequencing to shed light on: (i) their gut microbiota structure; (ii) how bacteria may interact among them; and (iii) predicted shifts in bacterial metabolic functions associated with the observed structural changes. Our findings revealed that Mycoplasma dominated the GI microbiome in both species. However, the structure of the bacterial communities differed significantly in spite of considerable intraspecific variation. This resulted from changes in predominant species composition in each GI microbiota, suggesting host-specific adaptation of bacterial lineages to these sympatric abalone. We hypothesize that the presence of exclusive OTUs in each microbiota may relate to host-specific differences in competitive pressure. Significant differences in bacterial diversity were found between species for the explored metabolic pathways despite their functional overlap. A more diverse array of bacteria contributed to each function in HC, whereas a single or much fewer OTUs were generally observed in HF. The structural and functional analyses allowed us to describe a significant taxonomic split and functional overlap between the microbiota of HF and HC abalone.

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Spatial and temporal scales at which processes modulate genetic diversity over the landscape are usually overlooked, impacting the design of conservation management practices for widely distributed species. We examine processes shaping population divergence in highly mobile species by re-assessing the case of panmixia in the iconic olive ridley turtle from the eastern Pacific. We implemented a biophysical model of connectivity and a seascape genetic analysis based on nuclear DNA variation of 634 samples collected from 27 nesting areas. Two genetically distinct populations largely isolated during reproductive migrations and mating were detected, each composed of multiple nesting sites linked by high connectivity. This pattern was strongly associated with a steep environmental gradient and also influenced by ocean currents. These findings relate to meso-scale features of a dynamic oceanographic interface in the eastern tropical Pacific (ETP) region, a scenario that possibly provides different cost-benefit solutions and selective pressures for sea turtles during both the mating and migration periods. We reject panmixia and propose a new paradigm for olive ridley turtles where reproductive isolation due to assortative mating is linked to its environment. Our study demonstrates the relevance of integrative approaches for assessing the role of environmental gradients and oceanographic currents as drivers of genetic differentiation in widely distributed marine species. This is relevant for the conservation management of species of highly mobile behaviour, and assists the planning and development of large-scale conservation strategies for the threatened olive ridley turtles in the ETP.

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For highly mobile species that nevertheless show fine-scale patterns of population genetic structure, the relevant evolutionary mechanisms determining structure remain poorly understood. The bottlenose dolphin (Tursiops truncatus) is one such species, exhibiting complex patterns of genetic structure associated with local habitat dependence in various geographic regions. Here we studied bottlenose dolphin populations in the Gulf of California and Pacific Ocean off Baja California where habitat is highly structured to test associations between ecology, habitat dependence and genetic differentiation. We investigated population structure at a fine geographic scale using both stable isotope analysis (to assess feeding ecology) and molecular genetic markers (to assess population structure). Our results show that there are at least two factors affecting population structure for both genetics and feeding ecology (as indicated by stable isotope profiles). On the one hand there is a signal for the differentiation of individuals by ecotype, one foraging more offshore than the other. At the same time, there is differentiation between the Gulf of California and the west coast of Baja California, meaning that for example, nearshore ecotypes were both genetically and isotopically differentiated either side of the peninsula. We discuss these data in the context of similar studies showing fine-scale population structure for delphinid species in coastal waters, and consider possible evolutionary mechanisms.

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Withering syndrome (WS) is a chronic wasting disease affecting abalone species attributed to the pathogen Candidatus Xenohaliotis californiensis (CXc). Wild populations of blue (Haliotis fulgens) and yellow (H. corrugata) abalone have experienced unusual mortality rates since 2009 off the peninsula of Baja California and WS has been hypothesized as a possible cause. Currently, little information is available about the genetic diversity of CXc and particularly the possible existence of strains differing in pathogenicity. In a recent phylogenetic analysis, we characterized five coding genes from this rickettsial pathogen. Here, we analyze those genes and two additional intergenic non-coding regions following multi-locus sequence typing (MLST) and multi-spacer typing (MST) approaches to assess the genetic variability of CXc and its relationship with blue, yellow and red (H. rufescens) abalone. Moreover, we used 16S rRNA pyrosequencing reads from gut microbiomes of blue and yellow abalone to complete the genetic characterization of this prokaryote. The presence of CXc was investigated in more than 150 abalone of the three species; furthermore, a total of 385 DNA sequences and 7117 16S rRNA reads from Candidatus Xenohaliotis californiensis were used to evaluate its population genetic structure. Our findings suggest the absence of polymorphism in the DNA sequences of analyzed loci and the presence of a single lineage of CXc infecting abalone from California (USA) and Baja California (Mexico). We posit that the absence of genetic variably in this marine rickettsia may be the result of evolutionary and ecological processes.

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