Gametogenesis, histological gonadal cycle and in vitro fertilization in the whitemouth croaker (Micropogonias furnieri, Desmarest, 1823)

The whitemouth croaker (Micropogonias furnieri) is a demersal teleostean fish inhabiting the Atlantic Ocean from northern Venezuela to southern Argentina. In terms of biomass, the whitemouth croaker is the dominant sciaenid in the Río de la Plata and constitutes an important renewable resource for the Uruguayan and Argentinean fisheries. In the present study, analyzed were the gametogenesis and histological gonadal cycle in female and male whitemouth croakers collected at the Uruguayan coast of the Río de la Plata, between March 1997 and February 1998. In addition, the experimental conditions required to obtain mature viable gametes and achieve in vitro fertilization in this species were investigated. These studies indicate that the whitemouth croaker inhabiting the Río de la Plata is a multiple spawner, which reproduces on the Uruguayan coast between October and February. In vitro studies showed that following activation, sperm remain motile for up to 40 min, and under optimal dilution conditions that they retain a high fertilization capability for 15 min. Taken together these results could support future aquaculture research and exploitation of this species.     

Morphometric and meristic spatial differences and mixed groups of the whitemouth croaker (Micropogonias furnieri (Demearest, 1823)) during the spawning season: implications for management

The aim of this work was to compare the morphometric and meristic characteristics of whitemouth croaker, Micropogonias furnieri, from two different areas: the Río de la Plata (to the west) and the oceanic coast (to the east) during the summer spawning season (December 1999), and to determine whether they constitute one demographic unit or independent management groups. Data from 966 whitemouth croakers were analysed for stock discrimination between areas. The results provided further evidence that the two cohorts differ significantly in these areas. However, an important misclassification of individuals was found. The morphometric variables that contributed more to discriminate the groups were mouth length, head length, horizontal eye diameter and length of the pectoral fin. Misclassified individuals from the western and eastern groups have shown that whitemouth croaker do not display high fidelity to their known spawning grounds. The well‐classified and misclassified individuals for the western and eastern groups were found to be mature and in spawning condition, representing between 82–84%, and 66–88%, respectively. These results support the hypothesis of contemporary gene flow between the Río de la Plata and coastal Atlantic populations. Despite the misclassified individuals, morphometrics presented in this study and genetic information originating from other studies show differences between Río de la Plata and oceanic groups, and predict the two‐stock hypothesis. Problems related arising from these mixed population groups and potential implications for managements are discussed.     

Phylogeography of the Endangered Franciscana Dolphin: Timing and Geological Setting of the Evolution of Populations

Pontoporia blainvillei (Gervais & d’Orbigny, 1844), the franciscana dolphin, is the most endangered small cetacean in the Western South Atlantic. It is an endemic species with a coastal and estuarine distribution that has been divided into four Franciscana Management Areas (FMAs). We used the mitochondrial DNA control region to conduct a phylogeographic analysis to evaluate the population structure of the franciscana and the influence of paleoceanographic events on its biogeographic history. We found nine populations along the entire distribution (Φ_ST?=?0.41, Φ_CT?=?0.38, p?<?10^–5), with estimated migration rates resulting in less than one female per generation. Populations from FMAIII and FMAIV in the south (including the Río de La Plata Estuary) showed higher long-term migration rates and effective population sizes than northern populations. The phylogeographic analysis supports the franciscana origin in the Río de La Plata Estuary, with further dispersal south and northwards. The first lineage split happened around 2.5 Ma, with lineage radiation throughout the Pleistocene until recent fragmentation events shaped current-day populations. We suggest that Pleistocene glaciations influenced the dispersion and population structure of the franciscana. Specifically, that the shift of the Brazil-Malvinas Confluence drove the dispersion northwards. Then, low sea-level periods caused either the isolation in estuarine refugia or local extinctions, followed by re-colonizations.

     

STRUCTURE,DEVELOPMENT, AND TAXONOMY IN THE GENUS LOPHOPHORA

Structural and developmental data indicate that Lophophora (Cactaceae) should be retained as a genus, which appears to be most closely related to Thelocactus (sensu lato). Within Lophophora morphological differences suggest that two species should be recognized. In the extensive northern population (Texas along the Río Grande to San Luis Potosí in Mexico) the tubercles are usually arranged as distinct ribs or elevated podaria, whereas in the restricted southern population (limited to the Mexican State of Querétaro) podaria and ribs are poorly developed or lacking and there are also differences in pollen structure. We believe that these two populations should be recognized as distinct species, L. williamsii and L. diffusa, respectively. We further believe that the latter represents the ancestral type.     

Pinus georginae (Pinaceae), a new species from western Jalisco, Mexico

Pinus georginae is described and illustrated as a new endemic species from the valleys in the southern basin of Río Ameca, Jalisco, western Mexico. It is closely related to Pinus praetermissa; however, after studying the cones and anatomy of the leaves in detail, characteristics were revealed that identify P. georginae as a distinct species.

---

Resumen  Se describe e ilustra Pinus georginae como una especie nueva, endémica de algunos valles intermontanos al sur del Río Ameca, Jalisco, en el Occidente de México. Los árboles se parecen a Pinus praetermissa; sin embargo, al estudiar con detalle los conos y la anatomía de las acículas lo ubican a Pinus georginae como una entidad biológica con categoría específica independiente.

     

Field observations on impact of egg parasiteTelenomus remus [Hym.: Scelionidae] on tobacco caterpillar,Spodoptera litura [Lep.: Noctuidae] in tobacco nurseries in Andhra Pradesh,India

The tobacco caterpillar,Spodoptera litura F. is a major pest in the tobacco nurseries causing damage by defoliation. Inundative releases were carried out with 650,000 parasites from 1st July, 1974 to 30th November, 1976. This paper reports the effectiveness from 1976 to 1979 of the parasite in reducing the population of tobacco caterpillar.Telenomus remus Nixon was found significantly effective in reducing the pest population at the peak of infestation in the site of release as compared to control nurseries where no parasites were released. However, the difference inSpodoptera population between the site of release and control was minimal during the last 1979 nursery season which suggests the necessity of inundative releases ofT. remus after every 2 years for effectively checking the population ofS. litura in tobacco nurseries.

---

Résumé La noctuelle du tabac,Spodoptera litura F. est un ravageur très important des pépinières de tabac du fait de ses défoliations. On a procédé à des lachers inondatifs de 650.000 parasites du 1^er juillet 1874 au 30 novembre 1976. Cette note indique l'action du parasite entre 1976 et 1979 dans la réduction des populations de chenilles du tabac. On a constaté queTelenomus remus Nixon a une activité significative dans la réduction des populations du ravageur au moment du maximum d'infestation dans le lieu de lacher par rapport aux pépinières témoins sans introduction de parasites. Cependant la différence des niveaux de population entre le lieu de lacher et le terrain a été minimum lors de la dernière période de plantation en pépinière en 1979, ce qui suggère la nécessité d'effectuer tous les 2 ans des lachers inondatifs deT. remus pour lutter efficacement contreSpodoptera dans les pépinières de tabac.

---

---

Paper presented at the 4th Tobacco Symposium held at Rajahmundry-533 105, India, 19–22 Jan. 1981.     

SHORT-TIME SCALE DEVELOPMENT OF A GYMNODINIUM CATENATUM POPULATION IN THE RIA DE VIGO (NW SPAIN)1

Wind direction and fresh water runoff determine the circulation pattern of the Ría de Vigo (NW Spain), which in turn influence the selection and distribution of its phytoplankton populations. Coastal winds with a south–southwesterly component reverse the positive estuarine circulation in the Ría, causing an off-shore to in-shore flow of surface waters and, consequently, the outflow of inner waters via deeper layers. We found that this reversal imposed a selective force on the phytoplankton population: diatoms, which could not counteract the sinking movement of the surface waters, were diminished, while dinoflagellates remained in the water column. From the end of September to the beginning of October 1993, an accumulation of Gymnodimium catenatum Graham was observed coinciding with an intrusion of coastal water induced by westerly winds which provoked a reversal in the circulation of the Ría. The slow reestablishment of the positive estuarine circulation pattern, which was due to a weak coastal upwelling and considerable fresh water runoff, allowed the population of G. catenatum to flourish.     

Spatial structure of genetic variation and primary succession in the pioneer tree species Antirhea borbonica on La Réunion

In habitats where colonization and extinction are recurrent, the distribution of gene frequencies among patches of suitable habitat may reflect the age structure of different populations. In this study, we quantify population genetic structure for a pioneer tree species, Antirhea borbonica, in a chrono-sequence of primary succession on the lava flows of the Piton de La Fournaise volcano (La Réunion). Using microsatellite loci and amplified fragment length polymorphism (AFLP) markers, we quantified genetic variation within and among populations for early- and late-succession populations in a landscape where extinction and recolonization are recurrent (the ‘Grand Brûlé’) and for late-succession populations in a more stable landscape. This study produced three main results. First, we detected no evidence that founder events increase genetic differentiation among colonizing populations; F_ST values among early- and among late-succession populations were similar. Second, we found no evidence for isolation by distance; genetic distance was not correlated with spatial distance within and among populations. Third, F_IS values are consistently high in all populations, despite the fact that A. borbonica populations are functionally close to dioecy and thus expected to have an outcrossing mating system. Multiple colonization events from different sources may limit differentiation among young populations and spatial isolation may enhance differentiation among late-succession populations. Ecological processes acting during colonization may create the conditions for spatial aggregation within pioneer populations, and thus contribute to the high F_IS values.     

Scale‐dependent post‐establishment spread and genetic diversity in an invading mollusc in South America

Aims Our study aimed to characterize the dispersal dynamics and population genetic structure of the introduced golden mussel Limnoperna fortunei throughout its invaded range in South America and to determine how different dispersal methods, that is, human‐mediated dispersal and downstream natural dispersal, contribute to genetic variation among populations. Location Paraná–Uruguay–Río de la Plata watershed in Argentina, Brazil, Paraguay and Uruguay. Methods We performed genetic analyses based on a comprehensive sampling strategy encompassing 22 populations (N = 712) throughout the invaded range in South America, using the mitochondrial cytochrome c oxidase subunit I (COI) gene and eight polymorphic nuclear microsatellites. We employed both population genetics and phylogenetic analyses to clarify the dispersal dynamics and population genetic structure. Results We detected relatively high genetic differentiation between populations (F_ST = ?0.041 to 0.111 for COI, ?0.060 to 0.108 for microsatellites) at both fine and large geographical scales. Bayesian clustering and three‐dimensional factorial correspondence analyses consistently revealed two genetically distinct clusters, highlighting genetic discontinuities in the invaded range. Results of all genetic analyses suggest ship‐mediated ‘jump’ dispersal as the dominant mode of spread of golden mussels in South America, while downstream natural dispersal has had limited effects on contemporary genetic patterns. Main conclusions Our study provides new evidence that post‐establishment dispersal dynamics and genetic patterns vary across geographical scales. While ship‐mediated ‘jump’ dispersal dominates post‐establishment spread of golden mussels in South America, once colonies become established in upstream locations, larvae produced may be advected downstream to infill patchy distributions. Moreover, genetic structuring at fine geographical scales, especially within the same drainages, suggests a further detailed understanding of dynamics of larval dispersal and settlement in different water systems. Knowledge of the mechanisms by which post‐establishment spread occurs can, in some cases, be used to limit dispersal of golden mussels and other introduced species.     

GENETIC STRUCTURE OF NATURAL POPULATIONS IN THE RED ALGAE GELIDIUM CANARIENSE (GELIDIALES,RHODOPHYTA) INVESTIGATED BY RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS1

Random amplified polymorphic DNA (RAPD) marker variation was analyzed in female gametophytes in natural populations of Gelidium canariense (Grunow) Seoane‐Camba ex Haroun, Gil‐Rodríguez, Diaz de Castro et Prud'Homme van Reine from the Canary Islands to estimate the degree and distribution of genetic variability and differentiation. A total of 190 haploid individuals were analyzed with 60 polymorphic RAPDs bands which produced 190 distinct multilocus genotypes. A high level of polymorphism was detected in all populations analyzed. Within‐population gene diversity ranged from 0.156 to 0.264. The populations on the island of Gran Canaria showed higher genetic variation than the other populations analyzed. The partitioning of molecular variance by analysis of molecular variance showed that most genetic variation resides within populations (68.85%). These results suggest that sexual reproduction is the predominant mode of reproduction for G. canariense gametophytic populations, and the main determinant in reaching high levels of genetic diversity. The Neighbor‐Joining tree and FCA analysis displayed two subclusters that correspond to the populations from the western islands (Tenerife, La Palma, Gomera) and the eastern island (Gran Canaria). In addition, we have detected a significant relationship between F_ST/(1?F_ST) and geographical distance consistent with data on water circulation and age of islands. The results obtained agree with an isolation by distance model, with gene flow from eastern to the western islands, and a high level of genetic differentiation between populations (F_ST=0.311, P<0.001).     

Climate as a driver of tropical insular diversity: comparative phylogeography of two ecologically distinctive frogs in Puerto Rico

The effects of late Quaternary climate on distributions and evolutionary dynamics of insular species are poorly understood in most tropical archipelagoes. We used ecological niche models under past and current climate to derive hypotheses regarding how stable climatic conditions shaped genetic diversity in two ecologically distinctive frogs in Puerto Rico. Whereas the mountain coquí Eleutherodactylus portoricensis is restricted to montane forest in the Cayey and Luquillo Mountains, the red‐eyed coquí E. antillensis is a habitat generalist distributed across the entire Puerto Rican Bank (Puerto Rico and the Virgin Islands, excluding St Croix). To test our hypotheses, we conducted phylogeographic and population genetic analyses based on mitochondrial and nuclear loci of each species across their range in Puerto Rico. Patterns of population differentiation in E. portoricensis, but not in E. antillensis, supported our hypotheses. For E. portoricensis, these patterns include: individuals isolated by long‐term unsuitable climate in the Río Grande de Loíza Basin in eastern Puerto Rico belong to different genetic clusters; past and current climate strongly predicted genetic differentiation; and Cayey and Luquillo Mountains populations split prior to the last interglacial. For E. antillensis, these patterns include: genetic clusters did not fully correspond to predicted long‐term unsuitable climate; and past and current climate weakly predicted patterns of genetic differentiation. Genetic signatures in E. antillensis are consistent with a recent range expansion into western Puerto Rico, possibly resulting from climate change and anthropogenic influences. As predicted, regions with a large area of long‐term suitable climate were associated with higher genetic diversity in both species, suggesting larger and more stable populations. Finally, we discussed the implications of our findings for developing evidence‐based management decisions for E. portoricensis, a taxon of special concern. Our findings illustrate the role of persistent suitable climatic conditions in promoting the persistence and diversification of tropical island organisms.     

Heterozygosity and effective size in laboratory populations ofAphidius ervi [Hym.: Aphidiidae]

Decline of allozyme variability in 7 laboratory populations ofAphidius ervi Haliday demonstrates that the effective population size is approximately one half the number of individuals used to renew the cultures each generation. Unequal reproductive contribution by individual females to subsequent generations is the most likely cause for this phenomenon.

---

Résumé La diminution de la variabilité des allozymes dans 7 populations de laboratoire deAphidius ervi Haliday montre que l'importance des effectifs des populations correspond approximativement à la moitié du nombre d'individus utilisés pour renouveler l'élevage à chaque génération. Une participation inégale à la reproduction des individus femelles aux générations successives est la cause la plus probable de ce phénomène.

     

Patterns of genetic differentiation in the <Emphasis Type="Italic">Gymnogeophagus gymnogenys</Emphasis> species complex,a neotropical cichlid from South American basins

The neotropical cichlid genus Gymnogeophagus is distributed in the Río de la Plata basin and in Dos Patos and Merín coastal lagoons on the border between Uruguay and southern Brazil. A phylogeographic approach based on mitochondrial cytochrome b analysis was performed to assess the patterns and processes of differentiation in this taxon. Gymnogeophagus gymnogenys showed high haplotype diversity (H = 0.992) and corrected mtDNA genetic distances ranged from 0 to 5.3%. Our analyses yielded robust support for the existence of four monophyletic groups within G. gymnogenys from the analyzed basins. No correlation between the aforementioned clades and geographic structure was found, since individuals belonging to different phylogenetic clades inhabit the same locality. The phylogeographic approach presented here showed that these four phylogroups (1, 2, 3 and 4) were sister groups. Our present findings would corroborate that G. gymnogenys could be integrated by different phylogenetic lineages, showing an explosive differentiation pattern and confirming the hypothesis that this taxon constitutes a species complex.     

Presence of <Emphasis Type="Italic">Ixodes neuquenensis</Emphasis> Ringuelet, 1947 (Acari: Ixodidae) on the endangered Neotropical marsupial Monito del monte (<Emphasis Type="Italic">Dromiciops gliroides</Emphasis> Thomas, 1894, Microbiotheria: Microbiotheriidae) at Chiloé Island,Chile

The presence of Ixodes neuquenensis (Ringuelet, Notas Mus la Plata 12:207–216, 1947) (Acari: Ixodidae) parasitizing populations of Dromiciops gliroides Thomas, 1894 (Microbiotheria: Microbiotheriidae) at Chiloé Island confirms that this tick species is established in Chile. No preference of the ticks for sex or age of the host was observed.     

Age validation and growth of Micropogonias furnieri (Pisces – Sciaenidae) in a temporally open coastal lagoon (South‐western Atlantic – Rocha – Uruguay) based on otolith analysis

In this work 228 individuals of the whitemouth croaker Micropogonias furnieri collected in the Rocha coastal lagoon (Uruguay) from October 1997 to September 1998 were analysed. The species formed annuli in the otolith (sagitta) associated with the opaque zone (narrow opaque annulus), mainly in early winter when water temperature decreased, and reached the lowest values in July–August. The period of greatest growth occurred from December to June, partially overlapping with the spawning period (December–March) and in coincidence with the increase in marginal increment. Growth parameters determined for all individuals were K = 0.19, L _∞ = 30.2 and t₀ = ?2.12. Annual growth increments showed that individuals grew rapidly and attained over 50% of their maximum observed size in the second year of life. In the third year, individuals attained sizes of first maturity at 11–12 cm less than estimates for the Río de la Plata spawning area and coastal areas of Brazil. The increment in length‐at‐age in the Rocha coastal lagoon was smaller than in individuals inhabiting the continental shelf (up to 50 m depth).     

Population structure of Squatina guggenheim (Squatiniformes,Squatinidae) from the south‐western Atlantic Ocean

Population genetic analyses based on both mitochondrial cytochrome b and the internal transcribed spacer 2 of recombinant (r)DNA genes were implemented to examine hypotheses of population differentiation in the angular angel shark Squatina guggenheim, one of the four most‐widespread endemic species inhabiting coastal ecosystems in the south‐western Atlantic Ocean. A total of 82 individuals of S. guggenheim from 10 sampling sites throughout the Río de la Plata mouth, its maritime front, the outer shelf at the subtropical confluence and the coastal areas of the south‐west Atlantic Ocean, were included. The analysis of molecular variance (AMOVA) based on the second internal transcribed spacer (its‐2) region supports that the samples from the outer shelf represent an isolated group from other sites. Historical gene flow in a coalescent‐based approach revealed significant immigration and emigration asymmetry between sampling sites. Based on the low level of genetic diversity, the existence of a long‐term population decline or a past recent population expansion following a population bottleneck could be proposed in S. guggenheim. This demographic differentiation suggests a degree of vulnerability to overexploitation in this endemic and endangered south‐west Atlantic Ocean shark, given its longevity and low reproductive potential.     

Contrasting patterns of morphological variation with dietary preferences in Micropogonias furnieri: insights from stable‐isotope and digestive‐trait analyses

The dietary preferences of populations of whitemouth croaker Micropogonias furnieri, which commonly inhabit estuarine and oceanic environments of the south‐western Atlantic Ocean, were investigated using stable‐isotope analysis and digestive traits, and compared with previous genetic and morphometric surveys of this species. Isotopic and C:N‐derived data suggested that individuals from coastal lagoons are the most differentiated from the remaining localities surveyed. In contrast, the analysis of the digestive traits did not show the same differentiation pattern. The overall correlation between isotopic, molecular and morphological variations suggests that genetic and phenotypic differences among populations are accompanied by differential resource use, supporting the idea that selective forces could be playing an important role in population differentiation.     

Reproduction strategies of <Emphasis Type="Italic">Daphnia pulicaria</Emphasis> population in a high mountain lake of Southern Spain

For three consecutive years, a population study of Daphnia pulicaria was undertaken in Río Seco Lake, a small high-mountain lake, in order to elucidate the reproductive strategies adopted by Daphnia in this system. Daphnia appears to colonize this lake every spring by hatching from ephippia and reproduce by means of subitaneous (non-diapausing) and ephippial (diapausing) eggs. D. pulicaria in this lake is an obligate parthenogenetic population. There is a short time period for subitaneous egg production and a much longer period for ephippial egg production. The contribution of subitaneous eggs to Daphnia population density and structure appears to be low. Diapause onset showed a high temporal synchronization in the three studied years in Río Seco Lake, and day-length emerged as the main cue triggering diapause onset and the main explanatory factor for the proportion of ephippial females observed. The development and reproduction of D. pulicaria in Río Seco Lake involves taking a gamble on resting forms to guarantee inter-annual Daphnia persistence in the lake, giving priority to investment in future generations. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Microsatellite loci in the stable fly,Stomoxys niger niger (Diptera: Muscidae) on La Réunion Island

Six polymorphic microsatellite markers have been isolated from a microsatellite‐enriched DNA library from the stable fly, Stomoxys niger niger. These loci exhibited five to 10 alleles per locus and an expected heterozygosity ranging from 0.57 to 0.81 in the studied populations from La Réunion Island (Indian Ocean). They should therefore be useful for the study of genetic diversity and population structure of S. niger. In addition, cross‐species amplification of four of these six loci in the closely allied species Stomoxys calcitrans produced interpretable results, two of which would be useful for population biology studies.     

Ontogenetic habitat preferences of the narrownose smooth-hound shark, Mustelus schmitti, in two Southwestern Atlantic coastal areas

The aim of this study was to determine the ontogenetic habitat preferences of the narrownose smooth-hound shark, Mustelus schmitti, in Río de la Plata and El Rincón coastal areas. There, canonical correspondence analyses of fishery research survey data showed that M. schmitti ontogenetic stages were differentially affected by depth, temperature and salinity. Neonates and juveniles were more abundant and remain in nearshore waters, suggesting the presence of nursery areas in which food availability and environmental conditions allow a faster growth. Adults M. schmitti presented different environmental associations mainly associated with depth and temperature. During non-reproductive season they were associated with deeper coastal waters. With the arrival of the reproductive season, adults migrate from deep to nearshore waters and show sexual segregation associated with pre- or post-mating behaviors. Hence, the year-round presence of neonates and juveniles and the seasonal occurrence of adults in nearshore waters make this habitat essential to M. schmitti population dynamics since key ontogenetic stages will be vulnerable if a direct impact occurs there.