Northern Trinidad Research Articles

Foraminiferal biofacies in the San José Calcareous Silt Member (Manzanilla Formation, Upper Miocene to Lower Pliocene) in the Manzanilla Bay area, north-east Trinidad, and their environmental significance

The Miocene–Pliocene Manzanilla Formation of northern Trinidad marks the arrival of the east-west flowing Orinoco River. Foraminifera were examined quantitatively in samples obtained at ∼5 m intervals from the lowest member of the formation, the San José Calcareous Silt Member, where exposed at eastern Manzanilla Bay and Point Noir. Recovery of Globorotalia merotumida indicates an age within the Globorotalia acostaensis Zone through Globorotalia margaritae evoluta Subzone, (N16–N19). Values of the information function (H) and the percentage of the total assemblage as planktonic foraminifera (%P), both traditionally used as palaeodepth indicators, were uncorrelated. The low values of H are indicative of freshwater influence. Cluster analysis revealed two major biofacies dominated by Pseudononion atlanticum and Hanzawaia carstensi respectively, for which similar values of mean H and mean %P suggest similar, inner to middle neritic palaeodepths, the P. atlanticum Biofacies indicating times of hypoxia. Entrained within these were rarer samples from a biofacies indicative of shallowing and increased freshwater input (Ammonia parkinsonia gr. Biofacies). An Amphistegina gibbosa Biofacies marked an interval in which water because sufficiently clear to support foraminifera symbiotic with algae, while a sample containing only Haplophragmoides wilberti was indicative of intertidal conditions. Some samples containing reddened foraminifera showed that deposition occasionally became very slow, but these were not limited to any one biofacies. The range of palaeodepths in which the San José Calcareous Silt Member was deposited is far less than in the underlying Brasso Formation, indicating that tectonic induction of transgressive–regressive cycles was slighter during San José times.

The rate of pregnancy in Trinidad and Tobago: A comparison between pregnant teenagers and pregnant adults registered at three health centers

Aim: This paper aims to determine the difference between the health and social conditions of women who had their first pregnancy as teenagers (13-19 years old) and those who had their first pregnancy during post-adolescence (20-41 years old). Materials and Methods : The results were based on a structured, 60-item interview schedule with 132 cases (71 teenagers and 61 women ≥ 20 year old) in Trinidad and Tobago. These cases comprised Afro-Trinidadians, Indo-Trinidadians, and Trinidadians of Mixed ancestry, who were all recruited by nurses in three health centers in Northern Trinidad, during the period October 2004 to October 2005. The main issues of concern regarding the respondents were history of stillbirths, abortion, contraceptive use, intended family size, marital status, and employment status. Data were analyzed, using Statistical Package for the Social Sciences (SPSS) 12.0. Results : While the study shows similarity between the two groups of respondents, in terms of their breast-feeding practices, there were differences regarding teenage mothers who experienced a higher level of unemployment (35%), single and common law relationships (81%), and lower contraceptive use (11.8%). The older mothers were more likely to be classified as unskilled (34.4%) compared to 22.5% for the teen group. Conclusions : The findings reveal that teenage pregnancy is considered a risk factor and has socio-economic implications regarding the lives of the mother and child in terms health, income, employment, and marital status.

Adding parasites to the guppy-predation story: insights from field surveys

Studies of phenotypic variation in nature often consider only a single potential selective agent. In such cases, it remains an open question as to whether variation attributed to that single measured agent might be influenced by some other unmeasured agent. Previous research has shown that phenotypic variation in the Trinidadian guppy (Poecilia reticulata) is strongly influenced by predation regime, and we here ask whether parasitism might represent an additional important selective agent shaping this variation. We performed a field survey of 26 natural guppy populations of known predation regime in northern Trinidad. We quantified levels of parasitism of guppies by the monogenean ecotoparasite, Gyrodactylus, and examined whether this parasite was associated with guppy body size or male colour. Spatial variation in Gyrodactylus parasitism was consistent between years, and parasite prevalence was generally, but not always, higher at high-predation sites than at low-predation sites. Consistent with previous work, predation regime was related to guppy size and some aspects of male colour, whereas parasitism showed few and only minor associations with the same traits. Moreover, a consideration of parasitism did not alter any interpretations regarding associations between guppy traits and predation regimes. These results suggest that parasitism, at least as quantified in the present study, does not play a major role in shaping variation in guppy body size or colour. Nevertheless, considerable variation in these traits, even within a predation regime, suggests the likely importance of other selective agents beyond just predation regime.

Parasite mediated homogenizing selection at the MHC in guppies

Understanding the selective forces influencing genetic diversity is a fundamental goal of evolutionary ecology. The genes of the major histocompatibility complex (MHC) play a key role in the adaptive immune response of vertebrates and thus provide an excellent opportunity to examine the agents of selection on a functionally important gene. Here we examine the genetic architecture of the MHC class IIB genes in 10 wild populations of guppies (Poecilia reticulata) in Northern Trinidad. We have previously shown that these populations are significantly less diverged at the class IIB locus than expected based on neutral (microsatellite) loci. We now survey infection by Gyrodactylus turnbulli and G. bullatarudis, common parasitic worms that infect guppies, as a potential agent of homogenizing selection. We used a genetic algorithm to partition both additive and non-additive genetic effects of the five most common MHC allele types as well as a rare allele category. Although we found no evidence for non-additive effects, across the populations we found that one allele type (the a-type) had a significant negative additive effect on parasite load. Thus, individuals who had more copies of the a-type allele were infected with fewer gyrodactylus than individuals with fewer copies of the allele. These results not only link parasite infection with MHC genotype, they provide a mechanism of homogenizing selection across these otherwise disparate populations.

Microsatellite genetic differentiation among populations of the Trinidadian guppy

Insight into the processes of evolutionary change can be obtained by studying the distribution of genetic diversity among populations. Such diversity can be shaped by historical colonization events, population connectivity and adaptation to local selection pressures. Here we examine genetic differentiation of Trinidadian guppies, Poecilia reticulata, by genotyping 373 individuals from 15 populations located in three drainages (northern coast, Caroni and Oropouche) with 7 microsatellite loci. Our data provide little evidence to support previous claims of two major genetic lineages of guppies in northern Trinidad but instead suggest a more complex pattern of gene flow among populations from different drainages. First, some of the populations in the Caroni drainage show genetic signatures similar to those in the Oropouche drainage. Second, the populations in the northern coast are all highly differentiated from those in either the Caroni or Oropouche drainages. Despite differing selection regimes owing to predation pressure, populations from upstream and downstream locales typically cluster together, albeit upstream populations consistently have less genetic variability than the corresponding downstream population. There is, however, no overall pattern of isolation by distance. We also find evidence that an artificially transplanted population from the Caroni drainage is successfully invading into other populations within the Oropouche system. Our analysis details the genetic and phylogeographic structure of Trinidadian guppies in the northern range and provides insight into evolutionary processes at different timescales that have shaped genetic heterogeneity in this fish.

Ecology and behaviour of the critically endangered Trinidad piping-guan Aburria pipile

From 1997 to 2001 we studied a group of 6 Trinidad piping-guans Aburria pipile, a crit- ically endangered species, in northern Trinidad. The group occupied a home range of 19 ha in highly disturbed secondary forest and around small farms, and often split into smaller groups. They spent 93.6% of the time in the forest canopy >5 m above ground and only 0.2% of the time on the ground (n = 48.1 h). In early morning (n = 18.7 h), they spent 80.3% of their time perched alert, 9.3% preen- ing, 3.9% flying, 3.6% walking, 2.4% feeding, 0.3% drinking, and 0.1% perched flapping. In late afternoon (n = 8.2 h), they spent 78.6% of their time perched alert, 12.8% preening, 3.7% walking, 3.0% feeding, 1.2% flying, and 0.7% drinking. At midday, they eluded observation. They foraged mostly on fruits (occasionally leaves or flowers) of 15 species of plants, with Virola surinamensis (Myristicaceae) constituting the primary item (33.3% of foraging bouts; n = 30). They drank water from epiphytic bromeliads. Drumming displays, produced mechanically by the wings in flight, were given intermittently throughout the morning and rarely in the afternoon. Singing occurred intermit- tently throughout the early morning and late afternoon. The song consisted of 3 to 7 plaintive whis- tles rising in pitch, delivered by lone individuals averaging 2.7 songs min -1 , in bouts of up to 30 min. Soft piping calls were usually given in a social context. Raised crest feathers appeared to be an aggressive display. Piping-guans rarely interacted with other species of birds. They were relatively unperturbed by human disturbance.

The persistence of Anolis trinitatis as a naturalized lizard in Trinidad against hybridization pressure with Anolis aeneus

Anolis aeneus and A. trinitatis were introduced to Trinidad before 1900, and A. extremus was a more recent introduction in the 1960s-1980s. The three species are of similar body size, and A. aeneus and A. trinitatis are known to hybridize in Trinidad. Detailed studies from the late 1960s indicated that A. aeneus was widespread but A. trinitatis was localized and apparently in decline due to hybridization pressure. In this study we examined all the known sites of A. trinitatis (and A. extremus ) in Trinidad, and many new sites. A. trinitatis remained abundant in and to the east of San Fernando in southern Trinidad. Two small populations remained in northern Trinidad, at one site in Port of Spain and at St Augustine, but A. trinitatis no longer occurred at most former sites there. A. trinitatis and A. aeneus had high niche overlap (0.99 or greater) for the three dimensions examined (substrate type and perch height and diameter). Both species were apparently still spreading into vacant habitats east of San Fernando. Of 12 sites from which A. trinitatis had disappeared, four had no anoles, four had sparse populations of A. aeneus , and only four had dense populations of A. aeneus . This pattern suggests that the decline of A. trinitatis is not related to hybridization with or competition from A. aeneus . An alternative hypothesis is presented, that A. trinitatis requires more vegetated habitats, which have been increasingly lost during urban development especially in northern Trinidad. A. extremus is apparently now extinct in Trinidad.

Inter‐population variation in multiple paternity and reproductive skew in the guppy

We use microsatellite loci to detail the multiple paternity patterns in broods from 10 wild populations of the guppy (Poecilia reticulata) found in Northern Trinidad. The populations span two major drainages comprising the Caroni and the Oropouche, and include sites that are characterized by either high or low predation. Across the populations the frequency of multiple paternity is high with 95% (range: 70%-100%) of broods having multiple sires. Broods have an average of 3.5 sires (range: 1-9) and a mixed-model analysis suggests that broods from high predation sites have marginally more sires than do those from low predation sites, but this is true only in the Oropouche drainage. There is no difference in sire number between predation sites in the Caroni drainage. Brood size, but not female body length, is correlated with the number of sires and the correlation cannot be attributed solely to the stochastic process associated with sperm competition and a 'fair raffle'. Within broods there is significant skew in reproductive success among males, which may reflect variation in sperm competitiveness or female choice. There is, however, no difference in the skew among populations from different predation regimes or drainages. Finally, high predation populations were characterized by increased genetic variability at the microsatellite loci, suggesting a larger effective population size. We discuss explanations for the high degree of multiple paternity but the general lack of any major differences among broods from ecologically different populations.

PARENTAL CARE IN THE NEOTROPICAL HARVESTMAN PHAREICRANAUS CALCARIFERUS (OPILIONES, CRANAIDAE)

Abstract Parental care in harvestmen may take several forms including egg hiding, egg guarding, egg transport and young guarding. In most species, one adult, usually the female, performs guarding of the young. From 9 July–3 August 2005, we made observations of parental care by adults of the Neotropical cranaid harvestman Phareicranaus calcariferus (Simon 1879) in northern and central Trinidad. Nine observations involved an adult female and young while three appeared to include both an adult female and male with young. The number of young present was inversely related to the size of the young, indicating that parental care in this species may occur over an extended period of time.

Passage of Ingested <I>Mansonella ozzardi</I> (Spirurida: Onchocercidae) Microfilariae Through the Midgut of <I>Aedes aegypti</I> (Diptera: Culicidae)

When virus and microfilariae are ingested concurrently by a mosquito, microfilariae (mf) may penetrate the mosquito midgut and introduce virus directly into the mosquito hemocoel, allowing mosquitoes to become infectious much sooner than normal and enhancing transmission of viruses by mosquitoes. Mansonella ozzardi (Manson) is a benign filarial nematode parasite of humans in Latin America and is transmitted by black flies (Diptera: Simuliidae) and biting midges (Diptera: Ceratopogonidae). Because M. ozzardi and dengue are sympatric, we wanted to know whether M. ozzardi mf had the ability to penetrate the midgut of Aedes aegypti (L.) (Diptera: Culicidae) and thus play a potential role in the enhancement of dengue transmission. To test this, the F1 progeny from locally collected Ae. aegypti were fed on M. ozzardi-infected human males in an endemic village in northern Trinidad. Mosquitoes were dissected at various times after feeding and examined for mf in the midguts and thoraces. Microfilariae penetrated the midguts of 43% of 63 mosquitoes that ingested mf. Overall, 11% of mf penetrated the midgut by 17 h after being ingested. The intensity of midgut penetration was positively correlated to the numbers of mf ingested. Because midgut penetration is a key requirement for mf enhancement to occur, the potential exists that M. ozzardi could be involved in the enhancement of dengue virus transmission.

Gametic isolation in guppies ( Poecilia reticulata )

Post-mating reproductive isolating mechanisms may be among the earliest reproductive barriers to emerge among incipient species. Trinidadian guppy, Poecilia reticulata, populations in the Caroni and Oropouche drainages in Northern Trinidad exhibit marked genetic divergence and provide an ideal system in which to search for these barriers. We inseminated virgin females with equal amounts of sperm from two males, a 'native' male from the female's own population and a 'foreign' male from the other drainage. Artificial insemination ensured that mating order and mate choice did not affect the outcome. Paternities were assigned to the resulting broods using microsatellite markers. As predicted, sperm from native males had precedence over foreign sperm. Moreover, this effect was symmetrical for both drainages. In contrast, we detected no native sperm precedence in controls, in which females received sperm from the same and another population within the same drainage. Our results show that gametic isolation can arise between geographically proximate, though genetically divergent, populations of a single species and highlight the potential role of this process in speciation.

Tadpole deposition behaviour in male stream frogs Mannophryne trinitatis (Anura: Dendrobatidae)

Male Mannophryne trinitatis transport their larvae on their backs to predator‐free pools and deposit them there. The experiments reported here investigated M. trinitatis male deposition behaviour in containers placed near a heavily fish‐populated stream at Mount Saint Benedict, northern Trinidad. Choice of deposition site was not related to height above or distance from the stream. The low mean number of tadpoles deposited in each container in the field and in a laboratory experiment indicated that most males tended not to deposit complete clutches in single pools. Deposition experiments in the laboratory with a choice of different‐sized containers showed that deposition was pool size dependent, with more tadpoles deposited in larger containers. Deposition behaviour when given a choice of containers with leaf litter (a source of food and shelter) and with no leaf litter showed no significant preference. Tadpoles grown in different water volumes with different food sources revealed that tadpole growth was best in larger water volumes containing leaf litter. Regular tadpole inspections at a pool in the field established that most tadpoles present were the result of downstream movement.

Gyrodactylus pictae n. sp. (Monogenea: Gyrodactylidae) from the Trinidadian swamp guppy Poecilia picta Regan, with a discussion on species of Gyrodactylus von Nordmann, 1832 and their poeciliid hosts

Gyrodactylus pictae n. sp. is recorded from Poecilia picta in heterospecific shoals with the guppy P. reticulata in Northern Trinidad. G. pictae is morphologically similar to G. turnbulli Harris, 1986, but the hamuli and marginal hooks are slightly smaller and more gracile. The toe and the point of the marginal hook have a distinctly different shape, providing the best morphological characters for distinguishing the two species. The rDNA ITS1 and ITS2 sequences differ from those of G. turnbulli (the closest relative) by >5, suggesting that these two taxa are not sibling species. The origin of the two species on poeciliids of the subgenus Micropoecilia is discussed, and it is suggested that this may represent a case of host-parasite co-evolution.

Three-Stage Slope Reversal in Northern and Central Trinidad and Its Effect on Megasequences in Cretaceous-Cenozoic Basins: ABSTRACT

Three-Stage Slope Reversal in Northern and Central Trinidad and Its Effect on Megasequences in Cretaceous-Cenozoic Basins: ABSTRACT

MITOCHONDRIAL DNA SEQUENCE VARIATION AMONG NATURAL POPULATIONS OF THE TRINIDAD GUPPY, POECILIA RETICULATA.

Guppies were sampled from eight populations representing four river drainage basins in northern Trinidad, and from one population on the nearby island of Tobago. For each individual, a 465 base pair (bp) segment of the control region of the mitochondrial genome was sequenced. The resulting DNA sequences were subjected to sequence divergence calculations and the populations were linked by maximum parsimony analysis to determine their phylogenetic relationships. Mitochondrial DNA (mtDNA) sequence variation was found both within and between river drainages, correlated with the geographic features of northern Trinidad. The variation observed exists primarily between drainages, particularly between the Oropuche drainage and all other Trinidad drainages examined. Estimates of time of divergence between guppy populations of different drainages, based on mtDNA sequence variation, ranged from 100,000 to 200,000 for the most recently separated populations and from 600,000 to 1.2 million years between the Oropuche populations and all others examined. Examination of fish from northeastern South America will be required to determine whether these populations differentiated in their present locations or were the result of separate invasions of Trinidad from different Venezuelan sources. However, genetic isolation of these populations appears to predate the current physical separation of the island of Trinidad from the Venezuelan mainland.

The rivers of northern Trinidad: conservation of fish communities for research: B. H. Seghers, in: River conservation and management, ed P.J. Boon & others, (Wiley), 1992, pp 81–90

The rivers of northern Trinidad: conservation of fish communities for research: B. H. Seghers, in: River conservation and management, ed P.J. Boon & others, (Wiley), 1992, pp 81–90

Recognition of Aphelandra glabrata (Acanthaceae) from Western South America, with Notes on Phylogenetic Relationships

Aphelandra glabrata is a highly distinctive member of the A. pulcherrima complex. Within this monophyletic group, A. glabrata belongs to a phylogenetic lineage that is marked by extrafloral (bracteal) nectary patches composed of numerous minute (<0.1 mm in diam.) glands. The species occurs in western South America, from central Colombia south into Peru and Bolivia. Aphelandra pulcherrima (with which A. glabrata has previously been combined) differs from this species in numerous features (e.g., nectary morphology, corolla vestiture, stigma morphology, and pollen morphology), and belongs to a different lineage within the A. pulcherrima complex. Aphelandra pulcherrima is a species of northern South America, occurring in northern Colombia, Venezuela, Trinidad, Guyana, and Surinam. Progress toward a monographic treatment of the approximately 40 members of the Aphelan- dra pulcherrima complex (sensu McDade 1984) requires recognition of A. glabrata Willd. ex Nees as distinct from A. pulcherrima Kunth. This change, together with recognition of the Cen- tral American plants formerly assigned to A. pulcherrima (Leonard 1938; Wasshausen 1975) as A. leonardii McDade (McDade 1982), clarifies the apparently extreme morphological variability within A. pulcherrima and reduces its range to northern Colombia, Venezuela, Trinidad, Guy- ana, and Surinam. Distinguishing these species further emphasizes the existence of at least two major monophyletic lineages within the A. pul- cherrima complex, with the newly recognized taxa A. glabrata and A. leonardii correctly placed in one lineage, and A. pulcherrima placed in the other, as described and figured below. Clarifi- cation of this taxonomic problem is especially important given that several floristic works cur- rently in progress in northern South America will near completion before a monographic treatment of the entire group can be published.

Comparative ecophysiology of CAM and C3 bromeliads. V. Gas exchange and leaf structure of the C3 bromeliad Pitcairnia integrifolia

Abstract Pitcairnia integrifolia is endemic to northern Trinidad and the Paria peninsula of Venezuela and is the only member of the bromeliad‐subfamily Pitcairnioideae in Trinidad. It is terrestrial with roots fully functional in water and solute uptake, grows on exposed steep rocky cliffs and can occur just above the spill zone of sea waves under continuous sea spray. Thus, it can be subject both to water stress, particularly during the dry season, and to salt stress.Gas exchange of P. integrifolia leaves was measured on a clear day in Trinidad. Uptake of CO2 and leaf conductance to diffusion of water vapour had two peaks during the light period, a larger one in the early morning and a smaller one in the late afternoon, which were separated by an extended midday depression of gas exchange. CO2 partial pressure in the leaf air‐spaces increased during the midday depression. Leaf temperatures reached a maximum of 51.6°C and leaf‐air water‐vapour‐concentration differences were also very high during the midday depression, when quantum fluxes were up to 2 mmol m−2 s−1 and higher. The midday depression is considered as a functional adaptation to temporary water stress.Although P. integrifolia is subject to sea‐spray, an internal osmotic pressure of only 0.91 MPa indicated that NaCl is not accumulated. Leaf epidermis cells are thick‐walled and have a prominent cuticle. The abaxial leaf surface with the trichomes is not wettable, and the trichomes apparently do not function in water and solute uptake. They cover the stomata densely and may create a favourable microenvironment around them. They also have a high reflectance. This does not prevent overheating of the leaves, but does reduce the photosynthetically active radiation penetrating to the mesophyll. The trichomes may thus contribute to the prevention of photoinhibition at high incident quantum flux.

A serosurvey for leptospirosis in Trinidad among urban and rural dwellers and persons occupationally at risk

A survey for leptospiral antibodies was made of 1,375 persons in northern Trinidad between mid-1977 and mid-1978. The subjects were employees in seven occupational categories thought to entail a high risk of exposure to leptospires, and members of the general population of three rural and two urban communities. They were questioned inter alia about their leisure and occupational activities, household water supply and effluent, and contact with animals. Leptospiral infection was found to be widespread in the general population but not primarily associated with employment. Among the occupational groups the highest prevalence of antibodies was found in sugar-cane workers (45% infected), while among the communities prevalence was highest in the rural village of Cacandee (37%) and lowest in Woodbrook (Port-of-Spain) (5%). Keeping cattle, hunting and walking barefoot in the countryside were significantly associated with leptospiral serology. Over-all, serogroups Icterohaemorrhagiae and Autumnalis each accounted for about 25% of the seropositives in the general population. Among the occupational groups Autumnalis was the most commonly found (36%). It accounted for 42% of the seropositive sugar-cane workers and 57% of the seropositive rice farmers.

"Ecological Release," Seasonal Variation in Food Supply, and the Hummingbird Amazilia Tobaci on Trinidad and Tobago

Resident populations of the Coppery—rumped Hummingbird, Amazilia tobaci, occupy the West Indian Islands of Trinidad and Tobago. Trinidad has 15 other hummingbird species, Tobago only 4 others. We predicted that A. tobaci on Tobago would have a broader feeding niche and a denser population than would A. tobaci on Trinidad. We monitored populations of Amazilia tobaci for 13 mo at study sites in the Arima Valley of northern Trinidad and in central Tobago. The two sites had nearly identical climates, and similar assemblages of flowers visited by hummingbirds. At both sites, food available to nectar—feeding birds varied &gt; 100 fold over the year. For 9 mo (December—August), neither A. tobaci population faced a severe food shortage. From September through November, nectar was scarce at both sites. During this period, Tobago A. tobaci faced only two other, uncommon species of nectar—feeding birds, which had very different feeding habits. The Trinidad population endured the food shortage along with six other hummingbird species. At this time Tobago A. tobaci utilized variously sized and shaped flowers of numerous plant species. On Trinidad, where many flowers were visited by the other hummingbird species, A. tobaci primarily used flowers that matched their bill size, which resulted in narrower feeding niche than on Tobago. These effects of "ecological release" on Tobago were apparent for only 3 mo, however, and when data for an entire year are compared there were few statistically significant contrasts between Tobago and Trinidad populations. At both sites, niche (diet) breadth responded in density—dependent fashion to changes in food density, broadening with high densities of A. tobaci relative to food, narrowing when food was abundant. Median values for niche breadth, population density, and population density per unit resource were not significantly greater on Tobago than on Trinidad. Ecological differences between the two populations during the food shortage may be linked to a phenotypic difference. We found no increase on Tobago in the intrapopulation variance of any morphological parameter important to feeding. However, Tobago, A. tobaci had longer wings than Trinidad conspecifics, resulting in lower wing disc loadings (ratio of body mass to area swept out by the wings). Among hummingbirds in general, low wing disc loading indicates a capacity to forage at a wide variety of flowers, which suggests that the Tobago population has undergone "within—phenotype nich expansion." Two experiments showed that individuals from the Tobago population of A. tobaci used a wide variety of artificial flowers, and a wide range of flower densities in field manipulations, than did conspecifics from Trinidad. The results suggest that occasional food shortages play a crucial role in the ecology and evolution of island populations, and that this might be undetected in short—term studies.