GAMETIC INCOMPATIBILITY BETWEEN SPECIES OF THE SEA URCHIN ECHINOMETRA ON THE TWO SIDES OF THE ISTHMUS OF PANAMA

The Pliocene rise of the Central American Isthmus has resulted in numerous “geminate pairs,” i.e., closely related species, one on each coast. Such species pairs can provide information on the evolution of isolating mechanisms in allopatry and on the relationship between genetic divergence and reproductive isolation in populations separated at a known time. The sea urchin genus Echinometra has one species, E. vanbrunti, in the eastern Pacific, and two, E. lucunter and E. viridis, in the Caribbean. E. viridis is morphologically distinct from the other two species, leading to the conclusion that E. lucunter and E. vanbrunti constitute a geminate pair. Allozyme data, on the other hand, place the speciation event of the two currently sympatric species after the rise of the Isthmus. We report fertilization experiments between the gametes of the three species performed to determine degree of reproductive isolation. Crosses between E. viridis and E. vanbrunti produce rates of fertilization almost equal to those manifested in homogamic crosses. Sperm of E. lucunter can fertilize eggs of the other two species, but few of its eggs permit fertilization by heterospecific sperm. Contrary to the predictions of the “speciation by reinforcement” hypothesis, degree of incompatibility between the allopatric E. lucunter and E. vanbrunti is higher than between the sympatric E. lucunter and E. viridis. Despite the incomplete and unidirectional nature of their gametic isolation, E. lucunter and E. viridis maintain their genetic integrities. Consideration of the likely phylogenetic relationships between the three species suggests that incompatibility of E. lucunter eggs with heterospecific sperm has evolved in the last 3.5 million years, after the rise of the Isthmus. There is no correlation between genetic divergence and strength of reproductive isolation, either within Echinometra, or among the geminate species pairs of echinoids that have been studied to date. Because recognition between echinoid gametes depends on the chemical compositions of a sperm protein and an egg glycoprotein, the appearance of gametic isolation would require only the fixation of a few mutations in each population on either side of a geographic barrier and could be independent of any other kind of genetic divergence. Thus, in animals with external fertilization, speciation need not be accompanied by major genomic reorganization.     

Reproductive periodicity of the echinoids Diadema and Echinometra on the two coasts of Panama

Patterns of reproductive periodicity in the regular echinoid species Diadema mexicanum A. Agassiz and Echinometra vanbrunti A. Agassiz from the Bay of Panama, and Diadema antillarum Phillipi, Echinometra lucunter (Linnaeus) and E. viridis A. Agassiz from the Caribbean coast of the Isthmus of Panama exhibit dissimilarities that reflect the differences of the environments they inhabit. Populations of the two species from the seasonal Bay of Panama display synchronous, well-defined, reproductive cycles. Spawning appears to be timed so that newly metamorphosed sea urchins, rather than larvae, can benefit from the increased food production concomitant with dry season upwelling. On the less seasonal Caribbean shore reproductive periodicity is less defined. Populations of Diadema antillarum and Echinometra lucunter from the vicinity of the Panama Canal show indications of periodicity, while those from a locality 20 km to the east display little tendency for synchrony between individuals. The much rarer E. viridis, on the other hand, maintains well-defined, population-wide cycles in both localities. It is suggested that in a constant environment the intensity of selection for synchrony between individual gametogenic cycles may be inversely proportional to population density.     

Adaptive evolution of sperm bindin tracks egg incompatibility in neotropical sea urchins of the genus Echinometra

Bindin is a gamete recognition protein known to control species-specificsperm-egg adhesion and membrane fusion in sea urchins. Previousanalyses have shown that diversifying selection on bindin aminoacid sequence is found when gametically incompatible speciesare compared, but not when species are compatible. The presentstudy analyzes bindin polymorphism and divergence in the threeclosely related species of Echinometra in Central America: E.lucunter and E. viridis from the Caribbean, and E. vanbruntifrom the eastern Pacific. The eggs of E. lucunter have evolveda strong block to fertilization by sperm of its neotropicalcongeners, whereas those of the other two species have not.As in the Indo-West Pacific (IWP) Echinometra, the neotropicalspecies show high intraspecific bindin polymorphism in the samegene regions as in the IWP species. Maximum likelihood analysisshows that many of the polymorphic codon sites are under mildpositive selection. Of the fixed amino acid replacements, mosthave accumulated along the bindin lineage of E. lucunter. Weanalyzed the data with maximum likelihood models of variationin positive selection across lineages and codon sites, and withmodels that consider sites and lineages simultaneously. Ourresults show that positive selection is concentrated along theE. lucunter bindin lineage, and that codon sites with aminoacid replacements fixed in this species show by far the highestsignal of positive selection. Lineage-specific positive selectionparalleling egg incompatibility provides support that adaptiveevolution of sperm proteins acts to maintain recognition ofbindin by changing egg receptors. Because both egg incompatibilityand bindin divergence are greater between allopatric speciesthan between sympatric species, the hypothesis of selectionagainst hybridization (reinforcement) cannot explain why adaptiveevolution has been confined to a single lineage in the AmericanEchinometra. Instead, processes acting to varying degrees withinspecies (e.g., sperm competition, sexual selection, and sexualconflict) are more promising explanations for lineage-specificpositive selection on bindin.     

Natural variation of carotenoids in the eggs and gonads of the echinoid genus, Strongylocentrotus: implications for their role in ultraviolet radiation photoprotection

We examined variability in carotenoid concentration in the gonads and eggs of four sea urchin species (Strongylocentrotus purpuratus, Strongylocentrotus franciscanus, Strongylocentrotus pallidus and Strongylocentrotus droebachiensis) to explore the possible role of carotenes as photoprotectants. Carotene concentrations were measured in gonads and gametes of each species, while in eggs the ultraviolet radiation (UV-R) sensitivity and self-shading capacity by carotenes were calculated. Mean concentrations of carotenes in gonads ranged from 0.13±0.017 mg g⁻¹ dw (S. purpuratus), 0.14±0.019 mg g⁻¹ dw (S. franciscanus), 0.29±0.079 mg g⁻¹ dw (S. pallidus) to 0.36±0.06 mg g⁻¹ dw (S. droebachiensis). In eggs, concentrations ranged from 0.026±0.003 to 0.09±0.034 mg g⁻¹ dw. UV-R sensitivity in eggs was quantified by measuring UV-R induced first-cleavage delay. Intra-specifically, cleavage delay varied significantly between individuals, and could be correlated with carotene concentration. Interspecific differences in cleavage delay and carotene concentrations were not correlated. Using the observed concentration of β, β-echinenone (which makes up between 82.4% and 94.9% of the total carotene concentration in the eggs) and a molar extinction coefficient of ε=13.7×10³ mol⁻¹ cm⁻¹ at 334 nm, we calculated self-shading efficiency in the eggs. Self-shading capacity (J₃₃₄) indicated that the eggs could only screen from 4.6% (J₃₃₄=0.046) down to 1.5% (J₃₃₄=0.015) of UV-R at 334 nm. While not sunscreens, we suggest that carotenes can photoprotective in echinoid eggs, probably by mitigating the effects of reactive oxygen species.     

Echinoid grazing as a structuring force in coral communities: Whole reef manipulations

To examine the effects of echinoid grazing on shallow water coral community structure, the entire Diadema antillarum Philippi population (> 3000 individuals) was eliminated from a patch reef in Discovery Bay, Jamaica W.I. in January 1974. All remaining regular echinoids, notably including Echinometra viridis A. Agassiz (> 7000 individuals), were removed from one-half of the same reef 6 months later.Where Echinometra was present, its grazing was highly patchy, even at densities of up to 50/m². On the other hand, the effects of grazing by Diadema were more uniformly distributed at equivalent or lower densities.Percent-cover of adult corals was enhanced in the presence of Echinometra viridis, however, it was greatly reduced in the absence of all echinoid grazing as a result of massive overgrowth by algae. Success of coral recruitment (density of coral spat) increased in the absence of Diadema due to the alleviation of biological disturbance imposed by this urchin's feeding activities. The presence of Echinometra viridis, even at the high densities naturally present on the reef, did not deter coral settlement.Coral diversity was highest in the presence of all echinoids, intermediate in the presence of E. viridis (without Diadema), and lowest in the absence of all echinoids. This was due to the disproportionately successful recruitment and resultant high relative abundance of Agaricia at low echinoid densities. Favia, Millepora, Helioseris and Acropora all exhibited universally low recruitment levels. Predation by Diadema and Echinometra is responsible for damaging larger coral colonies, particularly Porites.As echinoid species composition and density was altered, the species composition of benthic algae and associated invertebrates shifted. In this way, the array of species competing for space with coral spat shifted as did their competitive relationships. Major epifaunal competitors included spirorbid polychaetes, various foraminifera (particularly Gypsina), and sponges. Algal competitors included filamentous chlorophytes, corallines (e.g. Jania), and numerous other red algae; the species composition of algal competitors shifted through time. Competitive success in corals varied as echinoid density changed and was species-specific with respect to coral genus. Interspecific competition between coral spat (i.e., interspecific aggression via extracoelenteric digestion) was negligible under all treatments.The presence of Echinometra viridis in high densities (in the absence of Diadema) created conditions where growth and fusion in Agaricia spat were optimized. Under these conditions, fusion allows a young coral colony to attain a large enough size to survive damage incurred from grazing or from competitive overgrowth, decreasing the probability of whole-colony mortality during the early stages of development.     

A survey of Echinococcus species in wild carnivores and livestock in East Africa

We examined 71 faecal samples of carnivores from Queen Elizabeth National Park (QENP), Uganda, for eggs of Echinococcus species. Thirty-nine faecal samples contained taeniid eggs. For species diagnosis, DNA was isolated from a total of 1984 individual taeniid eggs. To differentiate eggs of Echinococcus felidis from other taeniid taxa (including the closely related Echinococcus granulosus sensu stricto), a restriction fragment length polymorphism (RFLP)-PCR of the mitochondrial nad1 gene was developed. As the faecal samples were taken from the environment, the host species was determined for all samples, except for one, by RFLP-PCR of the cob gene. Seven hundred and ninety-one of the 1984 eggs yielded a suitable PCR product. E. felidis was present in 34 of 47 samples from lions, none of 18 samples from leopards, and one of five samples from spotted hyenas. No Echinococcus taxon other than E. felidis was found, but three samples from lions contained eggs of Taenia regis. Two hydatid cysts of warthog origin from QENP were available for this study; molecular examination showed that one belonged to E. felidis, the other to E. granulosus (G1 strain). As a comparison of methods demonstrated that molecular diagnostic tools used for previous surveys of Echinococcus isolates in eastern Africa are not suitable to discriminate between E. felidis and E. granulosus sensu stricto, we re-examined 412 hydatid cyst samples of human, sheep, cattle, camel and goat origin from Kenya. Previous results were confirmed, as E. granulosus sensu stricto and Echinococcus canadensis G6/7 strain, but no E. felidis was found among these samples. In conclusion, we provide evidence that E. felidis is a frequent parasite of lions in Uganda, and possibly also occurs in hyenas. Additionally, we show that warthogs interact as intermediate hosts for E. felidis. We did not find evidence that E. felidis is present in eastern Africa outside conservation areas.     

Preliminary observations of spawning behavior of white-streaked grouper (Epinephelus ongus) in an Okinawan coral reef

Epinephelus ongus forms spawning aggregations at specific reef sites at Okinawa. The aim of the present study was to describe the spawning behavior of E. ongus based upon underwater video imagery. Epinephelus ongus spawning is usually paired with courting males and females rushing upwards towards the surface during the spawning ascent, with a subsequent release of eggs at the apex of the ascent. In two of four spawning events we observed, however, the ascending pair was joined by additional males. Fish eggs collected at the site were identified as those of E. ongus and confirmed that this species spawns mainly at night during a slack tide. This study is the first documentation of E. ongus spawning behavior in the field.     

Cultivation of shear stress sensitive and tolerant microalgal species in a tubular photobioreactor equipped with a centrifugal pump

The tolerance to shear stress of Tetraselmis suecica, Isochrysis galbana, Skeletonema costatum, and Chaetoceros muelleri was determined in shear cylinders. The shear tolerance of the microalgae species strongly depends on the strain. I. galbana, S. costatum, and C. muelleri exposed to shear stress between 1.2 and 5.4 Pa resulted in severe cell damage. T. suecica is not sensitive to stresses up to 80 Pa. The possibility to grow these algae in a tubular photobioreactor (PBR) using a centrifugal pump for recirculation of the algae suspension was studied. The shear stresses imposed on the algae in the circulation tubes and at the pressure side of the pump were 0.57 and 1.82 Pa, respectively. The shear stress tolerant T. suecica was successfully cultivated in the PBR. Growth of I. galbana, S. costatum, and C. muelleri in the tubular PBR was not observed, not even at the lowest pumping speed. For the latter shear sensitive strains, the encountered shear stress levels were in the order of magnitude of the determined maximum shear tolerance of the algae. An equation was used to simulate the effect of possible damage of microalgae caused by passages through local high shear zones in centrifugal pumps on the total algae culture in the PBR. This simulation shows that a culture of shear stress sensitive species is bound to collapse after only limited number of passages, confirming the importance of considering shear stress as a process parameter in future design of closed PBRs for microalgal cultivation.     

Egg production and early development of Thysanoessa inermis and Euphausia pacifica (Crustacea: Euphausiacea) in the northern Gulf of Alaska

Early life history patterns were studied in the dominant euphausiids from the northern Gulf of Alaska (GOA) in 2001-2004. Gravid females of Thysanoessa inermis were observed in April and May. Brood size varied from 10 to 1021 eggs with an average of 138 ± 19 (95% CI) eggs female^− 1. Most gravid females started to release eggs within the first 2 days of incubation. The average number of eggs released per female was similar in incubation Day 1 and 2, but significantly smaller on Day 3 and 4. About 25% of the females were continuously releasing eggs over 3 days rather than producing a single distinctive brood. In contrast, gravid females of Euphausia pacifica were observed from early July through October. Most gravid females released eggs on the first day of observation, while only 2% of females produced eggs repeatedly. Brood size varied from 20 to 246 eggs with an average of 102 ± 12 (95% CI) eggs female^− 1. The relationship between E. pacifica brood size and ambient chlorophyll-a concentration was sigmoidal (r² = 0.73), with food saturated brood size of 144 ± 14(SE, P < 0.001) eggs, and half-saturation occurring at 0.46 ± 0.02(SE, P < 0.001) mg chlorophyll-a m^− 3. The average interbrood interval of E. pacifica reared at 12 °C and satiated food conditions in the laboratory was ∼ 8 days, suggesting their potential individual fecundity in the GOA was 1148-1530 eggs per spawning season. Hatching and early development (from egg to furcilia stage) was studied under 5 °C, 8 °C and 12 °C. Hatching was nearly synchronous and lasted 3-6 h, depending on incubation temperature. Development times from egg to the first furcilia stage ranged between 20 and 33 days for T. inermis, and 15 and 45 days for E. pacifica at 12 °C and 5 °C, respectively.     

Factors influencing the embryonic development and hatchling size of the oceanic squid Illex coindetii following in vitro fertilization

Egg masses of oceanic squid accidently collected in the wild have been observed only from a few spawning events in aquaria, and as a consequence, the study of their embryos and hatchlings is very limited. Here, we used in vitro fertilization techniques to understand the abiotic factors that influenced egg development and hatchling performance of the ommastrephid squid Illex coindetii from the Mediterranean Sea. Egg and hatchling sizes of these ommastrephids are close to the minimum for cephalopod species, and therefore, short embryonic developmental periods were expected under a Mediterranean temperature regime. Low incubation densities and the use of antibiotics in the incubation medium resulted in relatively high survival rates to hatchling. Hatching time was inversely proportional to incubation temperature and ranged from 5 to 11 days at 21 °C and 13 °C, respectively. The addition of oviducal jelly to the eggs immediately after fertilization, followed by another addition at the beginning of organogenesis, resulted in better chorionic expansion, with an increase in egg diameter, delayed hatching and higher hatchling weight, which suggests a better use of yolk reserves. Larger hatchlings in length and weight also tended to be produced at low temperature, probably also due to better yolk absorption. As this species spawns all year round, size differences between summer and winter hatchlings may be suspected. In vitro fertilization techniques used in the laboratory proved to be useful in shedding some light on the early life of this oceanic squid. Further research is needed to elaborate on tests to predict gamete quality and to develop methods to avoid premature hatching.     

The appearance of beta-1,3-glucanase in hatching embryos of the sea urchin, Echinometra vanbrunti.

Two characteristics of fertilizing sea urchin eggs are the elevation of a fertilization membrane and the excretion of a β-glucanase. Of 13 species tested, one species, Echinometra vanbrunti, lacks both characteristics. No β-glucanase exists in the eggs and cleavage stages. However, β-glucanase appears at hatching and is secreted to the sea water during and after the hatching period. The enzyme may function in the hatching process. The hypothesis is presented that the β-glucanase excreted by eggs of other sea urchin species may function in the elevation of the fertilization membrane.     

Selective feeding by the echinoid,Evechinus chloroticus,and the removal of plants from subtidal algal stands in Northern New Zealand

Summary Feeding choice of the echinoid Evechinus chloroticus was examined for six fucoid and one laminarian species of algae. Three experiments were conducted to determine the algal choice by echinoids under controlled conditions. In the first experiment, the seven algal species were presented to echinoids in laboratory conditions. The second experiment had replicates of the algal species placed randomly on a subtidal rocky reef where echinoids were abundant and randomly dispersed. For the third experiment, which was also field-based, replicates of one highly-ranked species, Ecklonia radiata, were presented to naturally dispersed Evechinus. In addition, a series of controlled observations was used to examine the order in which echinoids removed algae from mixed species stands on subtidal boulders and to determine if this was related to the experimentally demonstrated choices of algal species.The results of the first two experiments showed that there were differences between algal species in the amount of material grazed by echinoids. Rankings of algal species from the field experiment were not correlated with rankings from the laboratory experiment. The order of removal of algal species from natural stands was correlated with the laboratory-based experimental rankings of algal species, but not with the rankings from the field-based experiment or with algal species availability. There were differences between algal species in their vulnerability to grazing by echinoids, as measured by regression analyses on the amount of material grazed from algal replicates vs. the number of attached echinoids. Within each species, echinoid numbers exerted a non-linear effect on the removal of algal material. In the third experiment, where only one species of algae was presented, the echinoids still distributed themselves non-randomly amongst replicates, aggregating on some samples.Data on the finer scale distribution of algal species over the entire subtidal reef on which these experiments and observations were conducted indicate that Evechinus are not often presented with a choice of adult plants of several different species in natural stands.The evidence from this study supports the conclusion that feeding preferences by echinoids are labile and do not clearly exert the major influence on the removal of plants from natural stands. Preference, as determined from experimental rankings of algal species, is only one of a number of factors which may affect the removal of algae by echinoids. Other important factors are the density of echinoids present, algal susceptibility to removal, and the distribution and abundances of the various algal species and echinoids relative to each other. It is suggested that algal life history characteristics may be unaffected by echinoids and that coevolutionary arguments are not appropriate for describing echinoid-algal interactions.     

Non-synchronous spawning behavior in laboratory reared amphioxus Branchiostoma belcheri Gray

Spontaneous spawning in amphioxus (Branchiostoma belcheri Gray) was observed in a tank and the characteristics of spawning were analyzed by video recording under infrared light conditions during summer of 2001. Everyday when spawning was observed, without exception a male first swam up from the bottom and released sperm near the water at the surface of the tank. The initiation time of the male spawning gradually became earlier as days passed. Spawning males and females individually swam up at various intervals and released gametes. However, at the population level, the spawning pattern of amphioxus was considered to be synchronous because both males and females intensively spawned around 90 min after the spawning of the first male. The act of releasing eggs or sperms of individuals was shorter than 10 min in most of the spawning animals.     

Primary gamete binding: Quantitative determination of its specificity in echinoid fertilization

The occurrence of primary gamete binding in homologous vs heterologous crosses of three species of echinoids was assayed quantitatively. The three sympatric echinoids, Lytechinus, Tripneustes, and Echinometra were chosen for this investigation because, under normal conditions, crossfertilization between these species is extremely low. In each of the three homologous crosses, large numbers of sperm become bound to the egg and are released, following the cortical reaction. A similar binding pattern does not occur in any of the six heterologous crosses, although we have previously shown that in these crosses sperm penetrate and undergo acrosomal reaction within the heterologous egg jelly [13]. The results of the present investigation demonstrate that primary gamete binding is the chief mechanism of reproductive isolation (species-exclusive event) of echinoid fertilization. Failure of reacted, heterologous sperm to undergo primary binding precludes subsequent interaction with the ovum and thus minimizes cross-fertilization.     

The ectosymbiont crab Dissodactylus mellitae-sand dollar Mellita isometra relationship

The presence of the ectosymbiont Dissodactylus mellitae on Mellita isometra was studied at Tybee Island in Georgia. The number of crabs found on sand dollars, stage of maturity, sex, numbers of eggs, and size of eggs produced by crabs were noted. The test diameter of sand dollars, and the number and diameter of eggs produced were also noted. Infestation rates of crabs on sand dollars varied over time. The maximum number of crabs found on a sand dollar was 10. The three types of population dispersion, random, uniform, and clumped, were observed for crabs on sand dollars throughout the sampling period. Clumped or gregarious settling was observed when juvenile crabs were abundant, uniform and random distribution when mature crabs were abundant. Female crabs were significantly larger than male crabs, with carapace width of the largest mature female crab being 4.6 mm and the largest male 3.1 mm. Crabs produced between 80 and 300 eggs from 0.188 to 0.291 mm in diameter. Bigger crabs produced significantly more eggs than smaller crabs. Sand dollar sizes were 50-110 mm, with a mode between 60 and 70 mm. The effect of crab burden on egg production in the sand dollar was time-dependent. The presence of crabs on sand dollars correlated with total egg production of sand dollars in May, the peak of the spawning season, with sand dollars carrying one or two crabs having a lower egg production than those without crabs. Overall, variation in egg size was attributed to variation among females followed by variation between seasons and crab burden.     

Reproductive biology of the antarctic opisthobranch Philine gibba Strebel

Monthly samples (August 1974 to February 1976) and cultured material have been used to describe ovotestis maturation, spawning, and larval development of the Antarctic opisthobranch Philine gibba Strebel. Ovotestis maturation took one year and mature individuals (mean shell length 12 ± 1.4 mm) spawned a single egg mass in April–May containing 975–4760 eggs, 379 μm in diameter.Development was non-pelagic but an active veliger was observed within the egg capsule. Juveniles (mean shell length 375 ± 55 μm), which hatched from August to October, resembled adults except for the presence of eye spots and an exposed shell. The mantle enclosed the shell by February when shell length was 890 ± 30 μm.     

Shallow Traces (Pits) in the Test of the Irregular Echinoid Echinocorys scutata Leske from the Chalk (Upper Cretaceous) of the United Kingdom

Specimens of epifaunal irregular echinoids in the Upper Cretaceous of northern Europe have been reported with patterns of circular, nonpenetrative parabolic pits, Oichnus paraboloides (Bromley), in the apical region. Specimens of Echinocorys scutata Leske from the Chalk at two sites in southeast England were commonly penetrated by this trace, generated by an indeterminate pit-forming organism. Pits commonly surround the apical system and, less commonly, occur within it; they occur preferentially anteriorly. Pits occur within plates, not along margins or sutures. Crosscutting of pits indicates that multiple spatfalls probably occurred. The host echinoid added new test plates adjacent to the apical system; thus, plates bearing O. paraboloides were moved abapically. The reduction in number of pits away from the apex, including those with echinoid tubercles reestablished on the base, indicates that, following death of an infester, the echinoid “reclaimed” and infilled them with calcite. The pit-former was most probably an unmineralized invertebrate that used E. scutata as a domicile which provided good access to food-rich currents for suspension feeding. Although the systematic position of the pit-former is unknown, similar infestations are known from other Upper Cretaceous echinoids and Mississippian crinoids.     

Assessing the In Situ Fertilization Status of Two Marine Copepod Species,Temora longicornis and Eurytemora herdmani; How Common Are Unfertilized Eggs in Nature?

We utilized an egg staining technique to measure the in situ fertilization success of two marine copepod species, Temora longicornis and Eurytemora herdmani from May to October 2008 in coastal Maine and correlated fertilization success with environmental conditions in their habitat. T. longicornis is a free spawning species that releases eggs into the ambient seawater after mating. In contrast, E. herdmani carries eggs in an egg sac until they hatch. The proportion of fertilized eggs within E. herdmani egg sacs was significantly higher than the freely spawned clutches of T. longicornis. This may be a result of the asymmetrical costs associated with carrying vs. spawning unfertilized eggs. T. longicornis frequently laid both fertilized and unfertilized eggs within their clutch. T. longicornis fertilization was negatively associated with chlorophyll concentration and positively associated with population density in their local habitat. The fertilization status of E. herdmani egg sacs was high throughout the season, but the proportion of ovigerous females was negatively associated with an interaction between predators and the proportion of females in the population. This study emphasizes that, in addition to population level processes, community and ecosystem level processes strongly influence the fertilization success and subsequent productivity of copepods.     

Development of the braconid wasp Cotesia flavipes in two Crambids, Diatraea saccharalis and Eoreuma loftini: Evidence of host developmental disruption

Cotesia flavipes is an important gregarious larval endoparasitoid of several crambid stem borers, including Diatraea saccharalis. The suitability of two crambid species, Eoreuma loftini and D. saccharalis, pests of sugarcane and rice in Texas, for C. flavipes development was tested. The effect of parasitization by C. flavipes on encapsulation response was assessed in vivo in both D. saccharalis and E. loftini. The results indicated that the parasitoid developed and emerged successfully in D. saccharalis larvae. Although E. loftini larvae were readily parasitized by C. flavipes parasitoids, no wasp larvae hatched from the eggs in this host because eggs were encapsulated by the host's hemocytes. The developmental fate of the E. loftini larvae with encapsulated parasitoids was variable. Most died as abnormal fifth instars or as post-wandering prepupae, while a few developed normally to the pupal stage. In vivo experiments, there was a significant reduction in the percent of beads encapsulated in parasitized larvae in both hosts. However, the percent of beads showing melanization decreased significantly in parasitized D. saccharalis larvae but did not differ significantly in parasitized or unparasitized E. loftini larvae. Our results showed that D. saccharalis is a suitable host for C. flavipes whereas E. loftini is an unsuitable host. This study indicated that lepidopteran stem borers that are taxonomically, behaviorally, and ecologically very similar can differ in their ability to encapsulate a parasitoid species.