Distribution of zooplankton during opposite tide fluxes in the lagoon complex of Chelem, Yucatan, Mexico]

Zooplankton was surveyed in a tropical lagoon system of the northern coast of the Yucatan Peninsula in high tide, December (1998) and low tide, March 1999 (northerlies season). Zooplankton biomass was measured, zooplankters were counted, and copepods were identified and quantified. Despite the fact that both months were influenced by winds from the North, they showed a different salinity gradient which developed a particular structure of the zooplankton community. Biomass tended to be accumulated in certain areas apparently because of the high residence time of water in Chelem, the forcing effect of the northerlies, and of the tidal current. Biomass values suggest a relatively high secondary production when compared with other systems of the Yucatan Peninsula. The distribution of the copepods Acartia lilljeborgii and A. tonsa is related to saline conditions and tidal flow. The overall faunistic and hydrologic data suggest that even during a single climatic season, the zooplankton community shows strong changes due to mesoscale hydrological processes.     

Association between Hyperoche martinezii (Amphipoda: Hyperiidae) and ctenophores from the Buenos Aires coast,Argentina (South-western Atlantic Ocean)

This survey examined the association between the hyperiid amphipod Hyperoche martinezii and ctenophores off the Argentinian coast (38°08′17″S, 57°31′18″W) through the evaluation of seasonality, prevalence and intensity of infection during an annual cycle. Medusae were also examined but only the ctenophores Mnemiopsis leidyi, Pleurobrachia pileus and Beroe ovata showed this association during the austral mid-spring to mid-summer. A total of 502 hyperiids were obtained; most (422 individuals) were larval stages, 53 juveniles and 27 adults. Mnemiopsis leidyi had the highest number of hyperiids with 98.6%, followed by P. pileus (0.80%), and B. ovata (0.60%). Total prevalence was 2.0 and intensity of infection ranged between 1 and 17 hyperiids per ctenophore. The host with highest prevalence was B. ovata (4.54), followed by M. leidyi (3.76) and P. pileus (0.1). Prevalence values had some correlations with the increase in the total length of B. ovata (r?=?0.480, P?=?0.006) and M. leidyi (r?=?0.501, P?B. ovata (r?=?0.425, P?=?0.017). The hyperiid was found in different parts of the host body: larval stages were found in the canal close to the subtentacular comb row and the stomodeum, whereas juvenile/adult stages were observed with a resting posture on the external surface of the ctenophores. The known geographic distribution of H. martinezii was extended; this finding represents the addition of three new hosts for this hyperiid.     

Hyperiid amphipods (Crustacea: Peracarida) in relation to a cold-core ring in the Gulf of Mexico

The species composition, distribution, and abundance of the hyperiid amphipods collected in March 1993 across a Gulf of Mexico cold-core ring (CCR) were analyzed. Day and night samples were collected by oblique tows (100 m to surface) with a plankton net. Hyperiids were represented by 56 species, 21 of which have not been recorded previously in gulf waters. The local oceanic community differs from that reported from adjacent neritic and neritic-oceanic areas of the Northwestern Tropical Atlantic. Overall, hyperiids were more abundant within (59% of total catch in org./1000 m³) than outside the CCR (41%). All inside CCR stations were sampled at night. Night outside vs. night inside CCR hyperiid faunas showed important differences in terms of species richness, composition and density. Cluster analysis indicated that day sta. 5 on the edge but outside the CCR was more similar to those stations inside the CCR (nighttime samples) than to the other daytime samples. Moreover, all the stations outside the CCR were clustered together independently of their day or night origin. It is suggested that the differences found were more related to differential conditions related to the CCR than to diel vertical migration. The analysis of three congeneric pairs with inverse CCR-related abundance and with known or inferred migratory patterns strengthened the idea that these pairs are probably separated by thermal preferences; also, their vertical migratory patterns seem to be abnormal inside the CCR. A relatively higher concentration of immature stages inside the CCR supports the idea that the enriched CCR waters constitute areas of increased production. Furthermore, this higher productivity enhances the chances of hyperiids to find their hosts, the gelatinous zooplankters, which are also more abundant inside the CCR.     

Genetic patterns and changes in availability of suitable habitat support a colonisation history of a North American perennial plant

• Climatic fluctuations during the Pleistocene influenced the geographical distribution of plant species across the southern region of California. Following an integrative approach, we combined genetic data analysis with Environmental Niche Models (ENMs) to assess the historical range expansion of Yucca schidigera, a long‐lived desert perennial native of the Baja California Peninsula.
• We genotyped 240 individuals with seven nuclear microsatellite to investigate genetic diversity distribution across 13 populations. Indeed, we used Environmental Niche Models to examine the changes on the distribution of suitable climatic conditions for this species during the LIG (~120 ka), LGM (~22 ka) and Mid Holocene (~6 ka).
• We detected high genetic diversity across Y. schidigera populations (A_R = 9.94 ± 0.38 SE; H_exp = 0.791 ± 0.011 SE) with genetic variation decreasing significantly with latitude (allelic richness: R ² = 0.38, P = 0.023; expected heterocigosity: R² = 0.32, P = 0.042). We observed low, but significant genetic differentiation (F_ST = 0.0678; P < 0.001) which was consistent with the parapatric distribution of the three genetic groupings detected by the Bayesian clustering algorithm. The ENMs suggest that suitable habitat for this species increased since the LGM.
• Our results support a range expansion of Y. schidigera across northwestern Baja California during the late Quaternary. Genetic data suggest that colonization of the current distribution followed a southward directionality as suitable climatic conditions became widely available in this region. High genetic variation across our sample suggests large historic effective population sizes for this section of the geographical range.

     

Expression of myostatin in the spotted rose snapper Lutjanus guttatus during larval and juvenile development under cultured conditions

In this study, the developmental expression pattern of myostatin (mstn) in the spotted rose snapper Lutjanus guttatus under culture conditions is presented. The full coding sequence of mstn from L. guttatus was isolated from muscle tissue, obtaining 1134 nucleotides which encode a peptide of 377 amino acids. The phylogenetic analysis indicated that this sequence corresponds to mstn‐1. mstn expression was detected in embryonic stages, and maintained at low levels until 28 days post‐hatch, when it showed a significant increase, coinciding with the onset of metamorphosis. After that, expression was fluctuating, coinciding probably with periods of rapid and slow muscle growth or individual growth rates. mstn expression was also analysed by body mass with higher levels detected in smaller animals, irrespective of age. mstn was also expressed in other tissues from L. guttatus, presenting higher levels in brain, eye and gill. In brain for instance, two variants of mstn were isolated, both coding sequences were identical to muscle, except that one of them contained a 75 nucleotide deletion in exon 1, maintaining the reading frame but deleting two conserved cysteine residues. Phylogenetic analysis indicated that this brain variant was also mstn‐1. The function of this variant is not clear and needs further investigation. These results indicate that mstn‐1 participates in different physiological processes other than muscle growth in fishes.     

Expression and activity of trypsin and pepsin during larval development of the spotted rose snapper Lutjanus guttatus

The present study aimed to describe and understand the development of the digestive system in spotted rose snapper (Lutjanus guttatus) larvae from hatching to 40 days post-hatch (dph). The mouth opened between 2 and 3 dph, at that moment the digestive tract was barely differentiated into the anterior and posterior intestine, although the liver and pancreas were already present. Gastric glands were observed until 20 dph, followed by the differentiation of the stomach between 20 and 25 dph. Trypsinogen expression and trypsin activity were detected at hatching, increasing concomitantly to larval development and the change in the type of food. Maximum levels of trypsinogen expression were observed at 25 dph, when animals were fed with Artemia nauplii, and maximum trypsin activity was detected at 35 dph, when larvae were fed with an artificial diet. On the other hand, pepsinogen gene expression was detected at 18 dph, two days before pepsin enzymatic activity and appearance of gastric glands. Maximum pepsin activity was also observed at 35 dph. These results suggest that in this species weaning could be initiated at an earlier age than is currently practiced (between 28 and 30 dph), since larvae of spotted rose snapper develop a functional stomach between days 20 and 25 post-hatch.     

Siphonophores of upwelling areas of the Campeche Bank and the Mexican Caribbean Sea

The siphonophore fauna off the Yucatan Peninsula and in the Mexican Caribbean Sea remains practically unknown. This communication describes the composition, abundance and distribution of Siphonophora during summer 1984 and spring 1985. The local distribution and abundance of siphonophores were found to be strongly influenced by upwellings, especially during the spring survey. Community analysis suggests that siphonophore populations around the upwellings are relatively homogeneous.     

Late postnaupliar development of Monstrilla sp. (Copepoda: Monstrilloida), a protelean endoparasite of benthic polychaetes

Polychaete specimens from Hawaii were infected by the copepod Monstrilla. The development of these protelean parasites has remained unstudied for more than a century. Three postnaupliar endoparasitic stages were obtained: copepodids CIII, CIV, and CV, the latter stage found previous to and during emergence. Copepodid development, including the body and appendages (antennules, legs 1–4, caudal rami), is described and analyzed. The feeding tubes and the exiting from the host are also described. In light of the recently proposed inclusion of monstrilloids among caligiform copepods, it was found that monstrilloid copepodid development diverges from caligiforms and other copepod groups in: (1) the segmentation of the urosome at CIII, (2) the early formation of a genital complex, (3) early completion of swimming legs setation, at CIII; (4) delayed segmentation of rami of leg 3 at CIII (vs. the usual two-segmented pattern), (5) loss of one exopodal seta of leg 1 at CIV, (6) full development of leg 1 endopod vs. usually vestigial condition in caligiforms; (7) earlier segmentation of leg 4 rami, and (8) stable interstage (CIII–CV) setation pattern of legs 3 and 4. Overall, monstrilloid development appears to have unique characters and their phylogenetic relations deserve further study.