Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles

Basic reproductive data from 21 green turtle (Chelonia mydas),8 leatherback (Dermochelys coriacea), 7 hawksbill (Eretmochelysimbricata), 7 olive ridley (Lepidochelys olivacea),6 loggerhead(Caretta caretta), 1 Kemp's ridley (Lepidochelys kempi), and1 flatback (Chelonia depressa) populations are provided. Someintraspecific and interspecific relationships between size ofnester and clutch, egg size and hatchling size are analyzed.Measurements of reproductive rates (=numbers of hatchlings perfemale per year) in 11 populations varied from 35 to 200 inan olive ridley and loggerhead colony, respectively. Nestingbehavior of each species is described in terms of type of nestingemergence and time spent on the nesting beach (=chelonery).The relatively large number of yolkless eggs laid by many leatherbacksand by some hawksbills invites further study. Some aspects ofsea turtle nesting behavior and reproduction are compared tothose of other chelonians.     

Evolutionary and Functional Aspects of Pituitary Gonadotropins in the Green Turtle, Chelonia Mydas

Information on the pituitary gonadotropins in Chelonia mydasrepresents some of the most complete data available for anyreptile and thus provides an important basis for evaluatingevolutionary processes in tetrapod endocrine physiology. Thetwo gonadotropins isolated from Chelonia pituitary glands showclear chemical and immunological homologies to mammalian follicle-stimulatinghormone (FSH) and luteinizing hormone (LH). However, receptorstudies and biological tests indicate that the functions ofthese hormones may be different in turtles and mammals. In particular,Chelonia LH shows an unusual ability to interact with FSH receptorsites and to stimulate physiological functions normally attributedto FSH. Results with Chelonia LH demonstrate that errors mayarise from using mammalian hormones to investigate reproductionin turtles. Measurements of endogenous gonadotropin levels inthe plasma of breeding and nesting Chelonia provide a differentperspective of the potential roles of the FSH and LH from thatobtained in physiological tests. In particular, FSH and LH secretionare markedly dissociated during the nesting cycle; FSH has onlya transient peak during oviposition, whereas LH, along withprogesterone, displays a pronounced "ovulatory" surge in theday following nesting. Preliminary studies with synthetic gonadotropicreleasing factors in Chelonia suggest that these may be usefulin inducing reproductive changes.     

The Ecological Strategies of Sea Turtles

By employing concepts such as "option" and "strategy" from gametheory, this study derives an ecologically-oriented dendrogramof the probable evolutionary history and the present relationshipsof sea turtles. An "armored tank" strategy is seen as differentiatingthe first ancestral testudines from the stem reptiles and providingenduring advantages while simultaneously imposing basic restrictionson all later forms. A "flipper" strategy is postulated as basicto development of the sea turtle line, again imposing limitationswhile conferring selective advantage. Modern sea turtle speciesare grouped into three lineages representing strategies of habitat-typeresource partitioning (a split-habitat, migratory pattern, aneritic residence pattern, and a pelagic residence pattern).Within the split-habitat, migratory group, further resource-partitioningby food-type separates the herbivorous Chelonia mydas populationsfrom omnivorous Eretmochelys imbricata and the (apparently)carnivorous Chelonia depressa. Herbivory is seen as integralto the split-habitat, migratory strategy and C. mydas is consideredthe most "traditional" species, with the migratory habit secondarilylost in the other two. At the same time, the enhanced philopatryselected for by the migration strategy is viewed as responsiblefor the fact that C. mydas seems to have the most active race-formationof the three species. Further habitat-type partitioning in theneritic group, together with food-type partitioning, separatesCaretta caretta from the two Lepidochelys species. L. kempiis represented as a consequence of Panamanian separation fromL. olivacea following the last establishment of the isthmusas a land barrier. The third, pelagic residence, strategy isrepresented by Dermochelys coriacea, with little further differentiationof the line. The paper attempts to show that the evolution ofsea turtles has been ecologically logical, that most conceivableniches for marine turtles are presently filled successfully,and that some predictions may be made with regard to gaps inour existing information.     

Insights into the habitat of Middle Permian pareiasaurs (Parareptilia) from preliminary isotopic analyses

Pareiasaurs were an abundant group of large herbivores during Middle and Late Permian times. The habitat of pareiasaurs has proven enigmatic, and ecological interpretations from anatomical and taphonomic data have included aquatic, semi‐aquatic to fully terrestrial lifestyles. Insight into the ecology of extinct taxa can also be gained from stable isotope analyses, and interpretations benefit from studies of multiple, coeval groups. Here, we report the first stable carbon and oxygen isotope analyses from the enamel, dentine and bone of pareiasaurs and contemporaneous therapsids (dinocephalians and therocephalians), in specimens recovered from the Permian Tapinocephalus to lower Pristerognathus Assemblage Zones of South Africa. Previous ecological inferences for dinocephalians (riparian to terrestrial) and therocephalians (terrestrial) are less ambiguous than reconstructions for pareiasaurs and provide an independent reference for interpreting stable isotope measurements. Oxygen isotopes of enamel carbonate were indistinguishable between pareiasaurs and therocephalians, which had higher values than dinocephalians. The data suggest that dinocephalians and pareiasaurs (megaherbivores) inhabited different ecological niches and that pareiasaurs may have shared a terrestrial habitat with therocephalians (carnivores). Our results agree with earlier suggestions of a terrestrial lifestyle among pareiasaurs and provide evidence of niche partitioning among large coeval Capitanian herbivores of South Africa.     

The Comparative Reproductive Physiology of Sea Turtles

Although the reproductive ecology of marine turtles has beenthe subject of numerous long-range studies, the reproductivephysiology of these unique animals is little known. Recently,however, preliminary anatomical and endocrinological studieshave provided a good basis on which to begin to attempt to explainseveral of their unusual biological systems. New findings relatedto the anatomy of Chelonia mydas and Lepidochelys olivacea arepresented. The female, although having a very massive pair ofsimultaneously functioning ovaries, appears in most ways verysimilar to other chelonians. Corpora hemorrhagica, corpora luteaand corpora atretica from active ovaries are briefly described.Ovulation coincides with a luteinizing hormone and progesteronesurge. Sperm are probably stored for the season after a singlemating period which appears to occur prior to the first ovulation.Males may also cycle and mating as well as nesting are seenas more or less seasonal. The seasonality could be controlledin part by melatonin or other endocrines from the sea turtle'smassive pineal complex. A hypothetical model for reproductionis presented in hopes of stimulating interest in physiologicalapproaches to the study of marine turtle reproduction.     

Historical Burden In Systematics And The Interrelationships Of 'Parareptiles'

The interrelationships within the clade comprised of turtles, pareiasaurs, and procolophonid-like taxa are investigated via a cladistic analysis incorporating 56 characters. A single most parsimonious tree was found (80 steps, c. i. = 0·8) in which the successive outgroups to turtles are: pareiasaurs, Sclerosaurus, lanthanosuchids, procolophonoids (=Owenetta, Barasaurus and procolophonids), and nyctiphruretians (= nycteroleterids). Thus, as suggested recently by other workers (Reisz, in Fischman, 1993) turtles are the highly modified survivors of a radiation of poorly-known reptiles commonly called ‘parareptiles’. Pareiasaurs are united with turtles on the basis of twenty unambiguous derived features which are absent in other basal amniotes (=‘primitive reptiles’) and reptiliomorph amphibians: for example, the medially located choana, enlarged foramina palatinum posterius, blunt cultriform process, fully ossified medial wall of the prootic, opisthotic-squamosal suture, lateral flange of exoccipital, loss of ventral cranial fissure, thickened braincase floor, ‘pleurosphenoid’ ossification, reduced presacral count, acromion process, trochanter major, reduced fifth pedal digit, and presence of transverse processes on most caudals. Recent phylogenetic proposals linking turtles with captorhinids, with dicynodonts, and with procolophonoids are evaluated. None of the proposed traits supporting the first two hypotheses is compelling. The procolophonoid hypotheses is supported by only one synapomorphy (the slender stapes). All other synapomorphies proposed in favour of the above groupings either occur in many other primitive amniotes, or are not primitive for turtles, or are not primitive for the proposed chelonian sister-group. Nyctiphruretus and Lanthanosuchids and nycteroleterids, often considered to be seymouriamorph amphibians, are demonstrated unequivocally to be amniotes. The ‘rhipaeosaurs’, currently considered to be pareiasaur relatives, are shown to be a heterogenous assemblage of seymouriamorphs, therapsids and nycteroleterids. The phylogeny proposed here indicates that many of the traits of the earliest known turtle, Proganochelys, previously interpreted as unique specialisations, also occur in pareiasaurs and other near outgroups of turtles, and must instead represent the primitive chelonian condition: for example, the wide parietals and the short quadrate flange of the pterygoid. The sequence of acquisition of chelonian traits is discussed: many features once thought to be diagnostic of turtles actually characterize larger groupings of procolophonomorphs, and must have evolved long before the chelonian shell appeared. These traits include most of the chelonian-pareiasaur synapomorphies listed above, and many others which characterize more inclusive groupings found in this analysis. In putting Proganochelys much closer to the main line of chelonian evolution, in elucidating the sequence of acquisition of chelonian traits, and in reducing greatly the number of differences between turtles and their nearest relatives, this study helps bridge one of the major gaps in the fossil record. The failure of previous cladistic analyses to identify correctly the nearest relatives of turtles is attributed to biased character selection, caused by an over-reliance on cranial characters deemed ‘important’ by earlier workers, and by a tendency to shoehorn ‘parareptile’ taxa into phylogenies derived from analyses restricted to ‘mainstream’ groups such as synapsids, diapsids, turtles, and ‘captorhinomorphs’. Many of the synapomorphies that resolve turtle origins are postcranial, and the three nearest outgroups to turtles are all highly bizarre groups which were dismissed as ‘too specialized’ by early workers and continued to be inadequately assessed even by workers using a cladistic framework.     

Pareiasaur phylogeny and the origin of turtles

The evolutionary relationship of all the valid species (and thus genera) of pareiasaurs are assessed through a phylogcnctic analysis of these taxa together with turtles, Owenetta, Barasaurus, Sclerosaurus, procolophonids, lanthanosuchids, nyctiphruretids, and nycterolctcrids. 128 os-teological characters were used, and almost all relevant taxa were examined. The results confirm that among these taxa, pareiasaurs and turtles form a robust clade, to the exclusion of all other taxa including procolophonids. However, pareiasaurs might not be the mono-phyletic sister group of turtles, as previously suggested. Rather, there is some evidence that pareiasaurs are paraphyletic with respect to (i.e. ‘ancestral to’) turtles. Among pareiasaurs, the early, large, heavily ossified forms such as Brady.saurus are most distantly related to turtles. These forms are characterized by rather smooth skulls, and dermal armour restricted to the dorsal midline. More closely related to turtles are forms such as Scutosaurus, Pareiasuchus, and Elginia. These taxa form a distinct clade of pareiasaurs, characterized by a very ‘mammallike’ pelvis, elaborate cranial ornamentation and a loose covering of osteoderms over the entire dorsum. The late, dwarf pareiasaurs Nanoparia, Anthodon, and Pumiliopareia are the nearest relatives of turtles. These forms exhibit otherwise uniquely turtle features such as a rigid covering of dermal armour over the entire dorsal region, expanded flattened ribs, cylindrical scapula blade, great reduction of humeral torsion (to 25^o), greatly developed trochanter major, offset femoral head, and reduced cnemial crest of the tibia. Thus, many features thought to be restricted to turtles (and thus to have evolved simultaneously with the turtle shell) actually arose earlier, at various points along the pareiasaurian stem lineage. The identification of the nature and sequence of anatomical changes leading to the origin of turtles, and the possibility that turtles are derived from dwarf pareiasaurs, should have important implications for speculations on the evolutionary biology of turtle origins.     

Inner ear morphology of diadectomorphs and seymouriamorphs (Tetrapoda) uncovered by high-resolution x-ray microcomputed tomography,and the origin of the amniote crown group

The origin of amniotes was a key event in vertebrate evolution, enabling tetrapods to break their ties with water and invade terrestrial environments. Two pivotal clades of early tetrapods, the diadectomorphs and the seymouriamorphs, have played an unsurpassed role in debates about the ancestry of amniotes for over a century, but their skeletal morphology has provided conflicting evidence for their affinities. Using high-resolution X-ray microcomputed tomography, we reveal the three-dimensional architecture of the well preserved endosseous labyrinth of the inner ear in representative species belonging to both groups. Data from the inner ear are coded in a new cladistic matrix of stem and primitive crown amniotes. Both maximum parsimony and Bayesian inference analyses retrieve seymouriamorphs as derived non-crown amniotes and diadectomorphs as sister group to synapsids. If confirmed, this sister group relationship invites re-examination of character polarity near the roots of the crown amniote radiation. Major changes in the endosseous labyrinth and adjacent braincase regions are mapped across the transition from non-amniote to amniote tetrapods and include: a ventral shift of the cochlear recess relative to the vestibule and the semicircular canals; cochlear recess (primitively housed exclusively within the opisthotic) accommodated within both the prootic and the opisthotic; development of a distinct fossa subarcuata. The inner ear of seymouriamorphs foreshadows conditions of more derived groups, whereas that of diadectomorphs shows a mosaic of plesiomorphic and apomorphic traits, some of which are unambiguously amniote-like, including a distinct and pyramid-like cochlear recess.     

The "Lost Year" Question in Young Sea Turtles

An adequate understanding of young sea turtle dispersal patternsis necessary for effective management of threatened or endangeredspecies. Such patterns are poorly understood, and the term "lostyear" has been adopted to emphasize this gap in sea turtle lifehistory information. Tag returns from pen-reared yearling seaturtles indicate ocean current dispersal. Evidence indicateshatchlings would be similarly dispersed by ocean currents. Feedingstudies with tank-held animals suggest that food resources areavailable in ocean currents for long-term sea turtle survival.Green turtle (Chelonia mydas) growth appears slow in nature.     

Reproductive Biology of Captive Green Sea Turtles Chelonia mydas

A captive colony of green sea turtles, Chelonia mydas, has beenmaintained and observed at a commercial sea turtle farm on GrandCayman Island, B.W.I., since 1973. Observations of this breedingcolony show that the mating and nesting behaviour of the captivegreen sea turtle is similar to that observed in wild populations.Evidence indicates that mating observed prior to a female'snesting in a given season determines the hatchabilityof thatseason's egg production. Annual per female egg production ofthe captive colony appears to be two to five times greater thanthat reported for wild colonies. Observations on the reproductivebiology of green sea turtles hatched and raised under farm conditionssuggests that the minimum age of sexual maturity is eight tonine years of age. The number of eggs per nest, the number ofnests per season per female and hatch rate tend to increasewith successive seasons nesting for these turtles reaching sexualmaturity.     

Gall Flies, Inquilines, and Goldenrods: A Model for Host-race Formation and Sympatric Speciation

Host shifts and subsequent host-race formation likely play amore common role in the speciation of herbivorous insects thanhas generally been recognized. Our studies of the interactionsof goldenrod host plants (Solidago: Compositae), the gall flyEurosta solidaginis (Diptera: Tephritidae), and the stem- andgall-boring Mordellistena convicta (Coleoptera: Mordellidae)provide behavioral, ecological, and genetic evidence of insecthost races that may represent incipient species formed via sympatricspeciation. Eurosta solidaginis has developed genetically differentiatedand reproductively isolated host races that are associated withthe ancestral host Solidago altissima and the derived host S.gigantea. Conventional wisdom suggests that shifts even to closelyrelated host plants are limited by host preferences or the inabilityto utilize a chemically and developmentally distinct host. However,our preliminary work with Eurosta from S. gigantea implies thathost choice and gall induction do not deter a shift to S. canadensis.The galling of Solidago by Eurosta created a new resource thathas led to a subsequent host range expansion by the stem-boringbeetle. Mordellistena convicta from stems and galls are geneticallydistinct and likely shifted from stems to galls. Beetles fromS. altissima versus S. gigantea galls exhibit assortative matingand higher preference for and/or performance on their natalhost. The present-day distributions of the Eurosta host racesand their behavioral isolating mechanisms do not suggest thatgeographic isolation was required for their formation; ratherthese characteristics suggest a sympatric mode of differentiation.Our findings lend credence to recent assertions that sympatricspeciation may be an important source of biodiversity.     

Pronounced ecophysiological clonal differences of two common freshwater ciliates, Coleps spetai (Prostomatida) and Rimostrombidium lacustris (Oligotrichida), challenge the morphospecies concept

Cell volume, growth and production rates of two common planktonicfreshwater ciliates, the prostomatid Coleps spetai and the oligotrichRimostrombidium lacustris, were investigated in clonal laboratorycultures. The clones were isolated from oligo-mesotrophic alpineLake Mondsee, Austria, during summer and kept in culture withthe small cryptophyte Cryptomonas sp. as food. All parametersinvestigated revealed significant clonal differences among bothspecies. The extent of the clonal differences was comparableto differences observed earlier between similar planktonic ciliatespecies. The ecological relevance of varying clonal growth rateswas evaluated using a simple numerical model. The model outcomesuggests that differences in growth rates by 10% may significantlyalter the clonal composition in the course of a ciliate peakin temperate lakes. The experimental results and the model outcomeare discussed in the context of the functional diversity offreshwater ciliates. It is concluded that the morphospeciesconcept, which is the most widely used concept by both ciliatetaxonomists and ecologists, may severely underestimate the ecologicalplasticity and the functional diversity of aquatic ciliates.     

NEW SPECIES OF THAIS (NEOGASTROPODA, MURICIDAE) FROM SINGAPORE, WITH A RE-DESCRIPTION OF THAIS JAVANICA (PHILIPPI, 1848)

The intertimdal gastropod Thais malayensis n.sp. (Neogastropoda,Muncidae) is described from Singapore and peninsular Malaysia.Although a common species, it may have been previously overlookedor mistaken for other species found in and near mangroves. Anotherpoorly known species, T javanica (Phdippi) may also have beenconfounded with the new species. New data on their soft parts,radulae, opercula, and egg capsule morphology are presentedto distinguish between these closely related species. (Received 26 February 1996; accepted 15 May 1996)     

Black holes, mate retention, and the evolution of ungulate leks

In some ungulates living in unstable herds, females in estrusleave their usual groups and join males defending mating territories.During the 12-24 h before mating, females commonly move severaltimes between males. These movements are commonly caused byharems being disrupted by young males or by overenthusiasticcourtship by the territorial male. When females leave a territorythey typically move to its nearest neighbor. Under these circumstances,clusters of territories can retain estrous females until theymate and leave the lek. This paper develops a model to investigatethe benefits of defending clustered versus dispersed territoriesto males and the consequences of variation in the rate of femalemovement between territories (P_m) and the tendency for femalesto move from one territory to a neighboring territory (a). Wherefemales move between territories at least once every 24 h (P_m< 0.04) and usually move to neighboring territories (a <0.5), the mating success of males is inversely related to thedistance from their territory to its nearest neighbor, and malesdefending clustered territories have higher mating rates thanthose defending dispersed territories. This process may be importantin the initial evolution of ungulate leks, which may resembleblack holes, attracting and retaining estrous females untilthey mate and their estrus ceases. It provides one possibleexplanation of the evolution of ungulate leks that does notrely on female preferences for mating with particular phenotypiccategories of males.     

Intercentrum versus pleurocentrum growth in early tetrapods: A paleohistological approach

A variety of vertebral centrum morphologies have evolved within early tetrapods which range from multipartite centra consisting of intercentra and pleurocentra in stem‐tetrapods, temnospondyls, seymouriamorphs, and anthracosaurs up to monospondylous centra in lepospondyls. With the present study, we aim to determine the formation of both intercentrum and pleurocentrum and asked whether these can be homologized based on their bone histology. Both intercentra and pleurocentra ossified endochondrally and periosteal bone was subsequently deposited on the outer surface of the centra. Our observations indicate low histological variation between intercentrum and pleurocentrum in microstructural organization and growth which inhibits the determination of homologies. However, intercentrum and pleurocentrum development differs during ontogeny. As previously assumed, the intercentrum arises from ventrally located and initially paired ossification centers that fuse ventromedially to form the typical, crescentic, rhachitomous intercentrum. In contrast, presacral pleurocentra may be ancestrally represented by four ossification centers: a ventral and a dorsal pair. Subsequently, two divergent developmental patterns are observed: In stem‐tetrapods and temnospondyls, the pleurocentrum evolves from the two dorsally located ossification centers which may occasionally fuse to form a dorsal crescent. In some dvinosaurian temnospondyls, the pleurocentrum may even ossify to full rings. In comparison, the pleurocentrum of stem‐amniotes (anthracosaurs, chroniosuchids, seymouriamorphs, and lepospondyls) arises from the two ventrally located ossification centers whereby the ossification pattern is almost identical to that of temnospondyls but mirror‐inverted. Thus, the ring‐shaped pleurocentrum of Discosauriscus ossifies from ventral to dorsal. We also propose that the ossified portions of the intercentrum and pleurocentrum continued as cartilaginous rings or discs that surrounded the notochord in the living animals.     

Lactate dehydrogenase genes of caiman and Chinese soft-shelled turtle, with emphasis on the molecular phylogenetics and evolution of reptiles.

L-Lactate dehydrogenase (LDH) cDNAs encoding for LDH-A(4) (muscle) and LDH-B(4) (heart) isozymes from caiman (Caiman crocodilus apaporiensis) belonging to the order Crocodilia and Chinese soft-shelled turtle (Pelodiscus sinensis) belonging to the order Chelonia were sequenced. The phylogenetic relationships of the newly determined cDNA and their deduced protein sequences, as well as the previously published sequences of vertebrate LDH isozymes, were analyzed by various phylogenetic tree construction methods. These results indicated that Chelonia is indeed more closely related to Crocodilia. The divergent times between caiman and alligator, turtle and soft-shelled turtle, and Chelonia and Crocodilia were estimated to be approximately 36, 100 and 177 million years, respectively.     

Bone microstructures and mode of skeletogenesis in osteoderms of three pareiasaur taxa from the Permian of South Africa

The extinct parareptilian clade of pareiasaurs was in the past often presented to constitute a morphocline from larger, less armoured forms to smaller, well armoured forms, indicating that the osteoderm cover became an increasingly prominent aspect in the post‐cranial skeleton of these animals. Here, we describe microanatomical and microstructural aspects of osteoderms of the three pareiasaur taxa Bradysaurus, Pareiasaurus and Anthodon from the Permian of South Africa. A generalized mode of osteoderm formation, consistent with intramembraneous skeletogenesis, is hypothesized to be present in all pareiasaurs. Few characters are shared between pareiasaur dermal armour and turtle shell bones and osteoderms. Otherwise, there is strong evidence from microanatomy and histology (i.e. absence of structures that formed via metaplasia of dermal tissue) that indicates nonhomology between pareiasaur dermal armour and the armour of living eureptiles. Analysis with bone profiler revealed no clear connection between bone compactness and lifestyle in the amniote osteoderm sample.     

ASPECTS OF THE LIFE CYCLE, POPULATION DYNAMICS,GROWTH AND SECONDARY PRODUCTION OF THE EDIBLE SNAIL HELIX LUCORUM LINNAEUS, 1758 (GASTROPODA, PULMONATA) IN GREECE

This paper examines the biology and ecology of Helix lucorumL. which lives in mainland Greece, as well as its growth andsecondary production. A demographic study revealed that (a)3 cohorts exist at any time during the year (when adults ofall generations belong to the same cohort) (b) egg-laying andhatching occur during the months of July and August respectively,(c) the most rapid growth takes place during spring. Study ofH. lucorum genitalia in relation to age showed that the snailsaxe sexually mature 3 years after hatching, when the largestdiameter of their shell (D) is equal to or greater than 35 mm Von Bertallanffy's method suggests that Helix lucorum may liveup to 14 years or more in order to reach its possible maximumsize (48.80 mm) The study of relative growth of D in relation to P_s (peristomesurface) of Helix lucorum shows that D grows faster than P_swhen D12.50 mm; juveniles change their growth rate when theirD arrives at 22.05 mm, and growth becomes slower when adultsarrive at 36.27 mm Annual secondary production calculated by the size frequencymethod gave a mean annual density of 3.39 individuals per m²,a mean annual crop (biomass) of 4.04 g-m^–2 and an annualproduction (P) of 5.02 g · m^–2. The annual turnoverratio (P//b) is equal to 1.24 (Received 23 June 1987;     

Predation risk, host immune response, and parasitism

Predation risk may affect the allocation priorities of limitingresources by potential prey. Investment in immune function shouldreceive reduced priority, when hosts are exposed to predatorsbecause of the costs of immune function. We tested this hypothesisby randomly exposing adult house sparrows, Passer domesticus,to either a cat, Felis catus, or a rabbit, Oryctolagus cuniculus,for 6 h while assessing their ability to raise a T-cell–mediatedimmune response to a challenge with phytohemagglutinin. Sparrowsexposed to a cat had a significant reduction of, on average,18% and 36% in T-cell response in two different experimentscompared with sparrows that were exposed to a rabbit. In a fieldexperiment with a barn owl, Tyto alba, or a rock dove, Columbalivia, placed next to a nest-box during laying, we found a meanreduction in T-cell–mediated immune response of 20%. Inmales, the reduction in cell-mediated immune response owingto cat exposure increased with increasing size of the badge,which is a secondary sexual character, but only during the breedingseason. In a third experiment, house sparrows were either exposedto a barn own, T. alba, or a rock dove, C. livia, and developmentof malarial infections was recorded during the following 6 weeks.Individual sparrows exposed to a predator had a higher prevalenceand intensity of Haemoproteus malarial infection than did controlindividuals. Therefore, exposure to predators reduced theirability of hosts to cope with parasitism mediated through effectson immune function.     

Cruzipain,a major Trypanosoma cruzi antigen,promotes arginase-2 expression and survival of neonatal mouse cardiomyocytes

An intense myocarditis is frequently found in the acute phase of Trypanosoma cruzi infection. Despite the cardiac damage, infected individuals may remain asymptomatic for decades. Thus T. cruzi may directly prevent cardiomyocyte death to keep heart destruction in check. Recently, it has been shown that Schwann cell invasion by T. cruzi, their prime target in the peripheral nervous system, suppressed host cell apoptosis caused by growth factor deprivation. Likewise, the trans-sialidase of T. cruzi reproduced this antiapoptotic activity of the parasite. In this study, we have investigated the effect of cruzipain, another important T. cruzi antigen, on survival and cell death of neonatal BALB/c mouse cardiomyocyte cultures. We have found that cruzipain, as well as T. cruzi infection, promoted survival of cardiomyocytes cultured under serum deprivation. The antiapoptotic effect was mediated by Bcl-2 expression but not by Bcl-xL expression. Because arginase activity is involved in cell differentiation and wound healing in most cell types and it favors parasite growth within the cell, we have further investigated the effect of cruzipain on the regulation of L-arginine metabolic pathways. Our results have revealed that cruzipain enhanced arginase activity and the expression of arginase-2 isoform but failed to induce nitric oxide synthase activity. In addition, the inhibition of arginase activity by N^G-hydroxy-L-arginine, abrogated the antiapoptotic action of cruzipain. The results demonstrate that cruzipain may act as a survival factor for cardiomyocytes because it rescued them from apoptosis and stimulated arginase-2. apoptosis; Bcl-2; Bcl-xL; nitric oxide synthase; nitric oxide