David A. Paz-García

Genetic Connectivity Patterns of Corals Pocillopora damicornis and Porites panamensis (Anthozoa: Scleractinia) along the West Coast of Mexico

Abstract: Genetic connectivity was studied in two scleractinian corals, Pocillopora damicornis (branching and broadcast spawner) and Pontes panamensis (massive and brooding type), along the Pacific coast of Mexico. Allelic diversity between adults and juveniles, the latter recruited after the El Niño—Southern Oscillation (ENSO) 1997–1998 event, was determined, and level of genetic connectivity among populations was assessed. There were no significant differences in allelic diversity between adults and juveniles from the same location. Seascape spatial genetic analysis suggested two or three clusters, depending on the species: (1) Bahías de Huatulco, (2) south of the Baja California Peninsula and Bahía de Banderas, and (3) locations in the Gulf of California. The most important barrier to gene flow was detected between Bahía de Banderas and Bahías de Huatulco and corresponds with a major coastal stretch of sandy beaches and lagoons. Moderate to high gene flow was found inside and at the entrance of the Gulf of California (Nem = 62–250), possibly favored by seasonal circulation patterns and sexual reproduction. In contrast, low gene flow was observed between southern populations and the rest of coastal Mexico (Nem < 1.7) based on high local recruitment and habitat discontinuity. A close genetic relationship of corals from the southern part of the Baja California Peninsula and severely damaged Bahía de Banderas coral communities confirmed that exchange of propagules could have taken place between the localities after the ENSO 1997–1998 event. Despite different reproductive strategies, both species showed similar patterns, suggesting the importance of surficial currents and habitat discontinuity to predict connectivity among coral reefs.

Testing the genetic predictions of a biogeographical model in a dominant endemic Eastern Pacific coral (Porites panamensis) using a genetic seascape approach

The coral fauna of the Eastern Tropical Pacific (ETP) is depauperate and peripheral; hence, it has drawn attention to the factors allowing its survival. Here, we use a genetic seascape approach and ecological niche modeling to unravel the environmental factors correlating with the genetic variation of Porites panamensis, a hermatypic coral endemic to the ETP. Specifically, we test if levels of diversity and connectivity are higher among abundant than among depauperate populations, as expected by a geographically relaxed version of the Abundant Center Hypothesis (rel-ACH). Unlike the original ACH, referring to a geographical center of distribution of maximal abundance, the rel-ACH refers only to a center of maximum abundance, irrespective of its geographic position. The patterns of relative abundance of P. panamensis in the Mexican Pacific revealed that northern populations from Baja California represent its center of abundance; and southern depauperate populations along the continental margin are peripheral relative to it. Genetic patterns of diversity and structure of nuclear DNA sequences (ribosomal DNA and a single copy open reading frame) and five alloenzymatic loci partially agreed with rel-ACH predictions. We found higher diversity levels in peninsular populations and significant differentiation between peninsular and continental colonies. In addition, continental populations showed higher levels of differentiation and lower connectivity than peninsular populations in the absence of isolation by distance in each region. Some discrepancies with model expectations may relate to the influence of significant habitat discontinuities in the face of limited dispersal potential. Environmental data analyses and niche modeling allowed us to identify temperature, water clarity, and substrate availability as the main factors correlating with patterns of abundance, genetic diversity, and structure, which may hold the key to the survival of P. panamensis in the face of widespread environmental degradation.

Switch between Morphospecies of Pocillopora Corals

Pocillopora corals are the main reef builders in the eastern tropical Pacific. The validity of Pocillopora morphospecies remains under debate because of disagreements between morphological and genetic data. To evaluate the temporal stability of morphospecies in situ, we monitored the shapes of individual colonies in three communities in the southern Gulf of California for 44 months. Twenty-three percent of tagged colonies of Pocillopora damicornis changed to Pocillopora inflata morphology during this time. This switch in identity coincided with a shift to a higher frequency of storms and lower water turbidity (i.e., lower chlorophyll a levels). Seven months after the switch, P. inflata colonies were recovering their original P. damicornis morphology. All colonies of both morphospecies shared a common mitochondrial identity, but most P. damicornis colonies undergoing change were at a site with low-flow conditions. This is the first in situ study to document switching between described morphospecies, and it elucidates the influence of temporal shifts in environmental conditions on morphologically plastic responses.

Morphological variation and different branch modularity across contrasting flow conditions in dominant Pocillopora reef-building corals

Pocillopora corals, the dominant reef-builders in the Eastern Tropical Pacific, exhibit a high level of phenotypic plasticity, making the interpretation of morphological variation and the identification of species challenging. To test the hypothesis that different coral morphospecies represent phenotypes that develop in different flow conditions, we compared branch characters in three Pocillopora morphospecies (P.damicornis, P. verrucosa, and P. meandrina) from two communities in the Gulf of California exposed to contrasting flow conditions. Morphological variation and branch modularity (i.e., the tendency of different sets of branch traits to vary in a coordinated way) were assessed in colonies classified as Pocillopora type 1 according to two mitochondrial regions. Our results can be summarized as follows. (1) Pocillopora type 1 morphospecies corresponded to a pattern of morphological variation in the Gulf of California. Overall, P.damicornis had the thinnest branches and its colonies the highest branch density, followed by P.verrucosa, and then by P.meandrina, which had the thickest branches and its colonies the lowest branch density. (2) The differentiation among morphospecies was promoted by different levels of modularity of traits. P.verrucosa had the highest coordination of traits, followed by P.damicornis, and P.meandrina. (3) The variation and modularity of branch traits were related to water flow condition. Morphology under the high-flow condition was more similar among morphospecies than under the low-flow condition and seemed to be related to mechanisms for coping with these conditions. Our results provide the first evidence that in scleractinian corals different levels of modularity can be promoted by different environmental conditions.

The complete mitochondrial DNA of endemic Eastern Pacific coral (Porites panamensis)

Abstract The mitogenome of the endemic coral Porites panamensis (Genbank accession number KJ546638) has a total length of 18,628 bp, and the arrangement consist of 13 protein-coding genes, 2 ribosomal RNA (rRNA) genes and 2 transfer RNA (tRNA) genes. Gene order was equal to other scleractinian coral mitogenomes.

Evidence of sexual dimorphism in skeletal morphology of a gonochoric reef coral

In the emerald coral Porites panamensis, the rates of elongation and calcification of colonies are higher in males than in females, probably because of the higher energetic demands of the latter in order to cope with the development of the large planulae produced throughout the year. This differing energetic demand could also be reflected in the sexual dimorphism of the calyces; hence, to test this hypothesis, 11 morphological traits of the corallite were assessed from 63 colonies that were collected in the southern Gulf of California, Mexico. Three traits showed statistical differences between sexes, enabling accurate distinction of males from females. Our results confirm for the first time the existence of external sexual dimorphism in a reef-building coral, opening the possibility that sex-related morphological differences may occur generally in gonochoric scleractinians. These findings can be very useful for the correct classification and characterization of recent and fossil records, helping to improve the historical and evolutive understanding of reef-building corals facing threats under environmental changes.