Nucleic acid indices of egg production in the tropical copepod Acartia sinjiensis

Two experiments were conducted to evaluate the effects of food and temperature on the nucleic acid content and egg production (and their relationship) of the tropical copepod Acartia sinjiensis. Experiment 1 evaluated the effect of food quality (as different algae species) on the relationship between nucleic acid content and egg production. In Experiment 2, the main and interaction effects of food type, food concentration and temperature on the total, Carbon and Nitrogen specific egg production and nucleic acid indices were evaluated in a factorial experimental design. Food quality, concentration and temperature significantly affected the nucleic acid content, egg production rate and the nucleic acid-egg production relationship of A. sinjiensis. RNA indices were correlated with egg production in females fed Pavlova salina, Tetraselmis chuii and Chaetoceros muelleri, but not in females fed Isochrysis aff. galbana. The slopes of the linear regressions of RNA indices as predictors of egg production were similar in females fed different algae species, suggesting that the slope of these relationships might be independent of food quality. The DNA content of females was significantly affected by food and temperature, suggesting that it is not a good index of cell number in this species. Nevertheless, the RNA:DNA ratio was as good a predictor of egg production as total RNA content. Egg production showed a weakly positive correlation with temperature. On the other hand, total, C- and N-specific nucleic acid indices had a strong negative correlation with temperature. In addition, temperature had a non linear effect on the slopes of the regression lines of RNA content and RNA:DNA ratio as predictors of egg production—slopes were similar at 25 °C and 30 °C, but significantly lower at 20 °C. Furthermore, the predictability of egg production was improved when the interaction term of nucleic acid indices with temperature was used instead of the nucleic acid indices alone in linear regression models. Our results suggest food quality has a limited influence on the nucleic acid-egg production relationship, and that temperature should be accounted for in models using nucleic acid indices as predictors of egg production in A. sinjiensis.     

Hydrozoan and protozoan epibionts on two decapod species, Liocarcinus depurator (Linnaeus, 1758) and Pilumnus hirtellus (Linnaeus, 1761), from Scotland

Crabs of the species Liocarcinus depurator and Pilumnus hirtellus, collected on the west coast of Scotland, showed hydrozoan and protozoan epibionts. The epibionts of Liocarcinus depurator were the protozoan Ephelota plana and the hydrozoans Clytia gracilis and Leuckartiara sp. The epibionts of Pilumnus hirtellus were the protozoans E. plana and Zoothamnium sp. For Liocarcinus depurator the number of Ephelota per crab fluctuated between 0 and 47 and the greatest number of suctorians were located on the chelipeds, carapace and anterior pereiopods. The hydrozoans, for Liocarcinus depurator, showed densities of 0-20 (Clytia gracilis on the second pereiopod) and 0-507 individuals per crab (Leuckartiara sp., principally on chelipeds, carapace and the fourth right pereiopod). For Pilumnus hirtellus, Ephelota plana showed densities between 3 and 56 individuals per crab, the greatest number of suctorians being located on the same areas as on Liocarcinus depurator. There was a density of 10-69 individuals per crab of Zoothamnium sp. on Pilumnus hirtellus (located on the carapace). Ephelota plana has not been observed previously as an epibiont on crustacea, nor had Zoothamnium sp. as an epibiont on Pilumnus hirtellus. Both hydrozoans, Leukartiara and Clytia, have not been previously described as epibionts on Liocarcinus depurator. Data about the morphological characteristics and distribution of these epibionts are included.     

The effect of food limitation on gonad development and egg production of the planktonic copepod Calanus finmarchicus

Calanus finmarchicus, one of the dominant copepods species of the North Atlantic, often encounters low food concentration or quality during the reproductive period; however, our knowledge on the effect of these conditions on reproduction processes is scarce. The present study combines experiments with histological observations to describe the response of C. finmarchicus to limited food focussing on (1) oocyte maturation processes, (2) gonad morphology, (3) egg production rates as a function of spawning frequency and clutch size, and (4) the fuelling of egg production by measuring carbon and nitrogen content of the females. In the laboratory, C. finmarchicus females were exposed to 0, 10, 50, 150 or >300 μg C l⁻¹ for several days. To account for food quality and season, reproductive activity was compared in April and July 1999 between females feeding on diatoms or dinoflagellates. The effect of feeding history was studied in February with females fed and starving prior to the experiment. Feeding conditions had severe effects on oocyte maturation process. Hence, egg production varied significantly with food concentration and quality, season and feeding history due to variation in both clutch size and spawning frequency. Clutch size differed by a factor of 2-4 between food limited and well fed females, and is thus an important parameter for modelling egg production. Changes in clutch size were related to changes of the number of maturing oocytes in the females gonads indicating that the latter can be used to precise the prediction of egg production from preserved samples. The proportion of females carrying at least some mature oocytes was relatively high at low food availability. Apparently, these females used internal body reserves as the carbon and nitrogen content decreased significantly under these conditions. These results indicate that C. finmarchicus embarks on the strategy to enable reproduction in all or many females of a population at low rates when feeding conditions are unfavourable.     

A case of germinoma in a limpet (Patella coerulea) (Patellogastropoda)

Germinoma is a gonadal neoplasm originating from progenitor cells in germinal epithelium. Frequently described in some populations of bivalve molluscs, to our knowledge, germinoma has never been reported in gastropods so far. In this paper we describe the histopathological findings of some atypical cellular masses, originating in the undifferentiated germ cell layer in the male gonads of a limpet (Patella coerulea), whose morphological appearance resembled that of a germ cell tumor. The abnormal, and independent growth with no evidence of maturation of the undifferentiated and atypical germ cells, the limited number of follicles involved (n < 10%) and the absence of tissue invasion, supported a diagnosis of Stage 1 germinoma.     

Reproductive response of Euterpina acutifrons in two estuaries of the Basque Country (Bay of Biscay) with contrasting nutritional environment

The reproductive response involving egg number and size was studied for the egg carrying copepod Euterpina acutifrons in two estuaries with different nutritional environment (Bilbao and Mundaka). To characterise the available food for copepods, the concentration of particulate organic matter (POM), the combined concentration (PGL) and proportion of particulate protein, carbohydrate and lipids and the concentration of chlorophyll a were measured in the <20 μm seston fraction. Data on female size (prosome length) and abiotic factors, such as temperature, salinity and oxygen saturation in water, were also obtained to relate them to reproductive and nutritional variables. Correlation and stepwise regression analyses indicated that temperature via female size was the main factor controlling brood volume in a temporal context, whilst the nutritional environment had a secondary role. Nevertheless, the nutritional environment caused noticeable between-estuary differences in the reproductive response of this species. ANOVA tests showed that E. acutifrons clutch size and brood volume were significantly bigger in the estuary of Bilbao, which was richer in both total (POM) and labile (PGL) organic particulate matter than the estuary of Mundaka. In contrast, egg size, female size and phytoplanktonic food quantity did not differ significantly between estuaries. These results suggest that the organic enrichment with particles of detritical-heterotrophic origin enhanced E. acutifrons clutch size and brood volume in Bilbao. Egg size was closely related to phytoplankton in both estuaries, but a clear trade-off between egg size and number per clutch was observed only in Mundaka. Thus, we suggest that the reduction of egg number in order to increase egg size might happen only under food-limiting conditions, but not in organically rich and quite constant nutritional environments such as found those in Bilbao.     

Grazing-filtration as feeding mechanisms in motile specimens of Crepidula fecunda (Gastropoda: Calyptraeidae)

Quantification of ingestion by grazing and by filtration in Crepidula fecunda showed that during the motile phase of the life cycle (<28 mm in shell length), the species depends on both feeding strategies to supply it's energetic requirements. This species improves the energetic quality of the material ingested by exercising preferential selection for organic material from all the materials that are available on the substrate, with an average organic enrichment of 13%. The ontogenetic change in the relative importance of grazing and filter feeding appear to be species-specific within the genus; some species have motile forms in earlier life stages which need to move about the substrate to obtain food and locate aggregations of conspecifics. After growing to about 28 mm in length, C. fecunda become sessile females and depend solely on filter feeding to meet their nutritional requirements.     

The influence of bioturbation by the sandprawn Callianassa kraussi on feeding and survival of the bivalve Eumarcia paupercula and the gastropod Nassarius kraussianus

Field observations and experimental evidence have shown that bioturbation by the southern African sandprawn Callianassa kraussi may significantly influence the abundance and distribution of the filter-feeding bivalve Eumarcia paupercula and the grazing gastropod Nassarius kraussianus. It was hypothesized that (1) sediment reworking by C. kraussi negatively affects microalgal growth on the sediment surface, leading to a reduction in food intake by N. kraussianus, (2) sediment deposited by C. kraussi will also diminish the food uptake of E. paupercula by interfering with its filtration mechanism. To test these hypotheses, manipulative field and laboratory experiments were undertaken in which N. kraussianus and E. paupercula were added to treatments with and without C. kraussi, and their survival and gut chlorophyll-a content measured. The effects of C. kraussi on sediment erodability and on condition of E. paupercula (tissue mass/shell length) were determined in a second experiment. In the presence of C. kraussi, (1) microalgal consumption by both N. kraussianus and E. paupercula was halved; (2) condition and survival of E. paupercula were significantly reduced but survival of N. kraussianus was unaffected; and (3) sediment erodability was increased. A significant negative relationship was established between sediment erodability and condition of E. paupercula. Evidently C. kraussi exerts a strongly negative influence on the feeding of E. paupercula and N. kraussianus, and this may explain the scarcity of these organisms in areas containing high densities of C. kraussi.     

Temporal scales of variation in settlement and recruitment of the mussel Perna perna (Linnaeus, 1758)

Population dynamics of many intertidal organisms are strongly affected by the abundance and distribution of larvae arriving on the shore. In particular, not only absolute numbers of settlers but also the degree of synchronisation of settlement can have a strong influence on whether density-dependent or density-independent processes shape adult shape populations. Temporal variation in rates of settlement and recruitment of the mussel Perna perna on the south coast of South Africa was investigated using a nested spatial design at different temporal scales. Variability in settlement at spring tides was examined at two temporal scales: lunar (to investigate the effect of state of the moon on settlement) and tidal (to investigate the influence of state of the tide on mussel settlement). Recruitment over neap tides was examined at one temporal scale, fortnight (to investigate the effect of date on mussel recruitment).Strong temporal variation was evident for both settlement and recruitment, but not at all time scales. Distinct peaks of settler/recruit abundance were observed during the lunar and neap tide studies. Recruitment intensity differed over the course of the year, and pulsing of recruitment was generally synchronised among locations. However, the strength of pulsing differed dramatically among locations, giving a significant interaction between fortnight and location. The finest temporal scale, investigated in the tidal study, did not reveal a significant effect of the state of the tide on settlement. The state of the moon (new or full) was not significant as a main factor (p = 0.052), although generally more settlers arrived on the shore during new moon. Phase of the moon appeared to have an effect on settler abundances, but only when and where densities were high.     

K~(+)、Cr~(6+)对网纹藤壶幼虫发育和存活的影响

以华南沿海污损生物群落优势种网纹藤壶(Balanus reticulatus)的幼虫为研究对象,探讨钾、铬2种金属离子对其幼虫存活及发育的影响。实验所用金属离子溶液是将K+和Cr6+母液添加到过滤消毒海水中配制。将活泼健壮的网纹藤壶无节幼虫置于上述溶液中,以亚心形扁藻(Platymonas subcordiformis)为饵料于30℃左右的黑暗环境中培养5d,镜检观察记录幼虫发育状况并进行统计分析。结果表明,K+对网纹藤壶幼虫发育和存活的影响均不明显;而Cr6+对幼虫发育具有一定的毒杀和抑制作用,不仅幼虫存活率低于对照组,而且金星幼虫所占百分率也低于对照组。     

The role of egg pod foam and rearing conditions of the phase state of the Asian migratory locust Locusta migratoria migratoria (Orthoptera, Acrididae)

Coloration phase state, morphometrical ratios and the numbers of mature oocytes of Locusta migratoria migratoria were examined in a series of experiments to determine the means by which phase characteristics are passed to the next generation. Washing with distilled water of eggs from egg pods laid by gregarious crowd-reared females resulted in solitarization of the hatchlings after their isolation, indicating that a factor present in eggs encapsulated in foam is causal to gregarization. Such locusts showed a significant shift towards the typical solitarious body coloration, morphometry and number of mature oocytes as compared to locusts resulting from unwashed eggs. Gregarious coloration, morphometrical ratios and oocyte numbers could be partially restored when hatchlings from washed eggs were regrouped. When gregarious locusts were reared in isolation, they showed a solitary body color, whereas, morphometry and oocyte numbers were not affected by isolation.     

Effects of food availability on larval development in the slipper limpet Crepidula onyx (Sowerby)

Effects of food availability on the larval survival and development of Crepidula onyx were studied in four experiments by feeding the larvae with different concentrations of the chrysophyte Isochrysis galbana and by starving the larvae for different periods of time. Food concentration had a clear impact on the survival, growth and development time of C. onyx veligers. Larval development occurred only at 10⁴ cells ml⁻¹ and higher algal concentrations. No shell increment was detected in the veligers cultured for 12 days at 10² cells ml⁻¹I. galbana or the blank control. At 10³ cells ml⁻¹, there was only a slight increase in shell length over 12 days. At 10⁴ cells ml⁻¹, about 40% of the larvae became competent in 18 days. At 10⁵ and 10⁶ cells ml⁻¹, more than 90% of the larvae reached competence in 7 days. Initial starvation negatively affected the larval development, but the sensitivity differed among parameters measured on day 5: lower survivorship was detected only for larvae that had suffered 3 days or longer initial starvation, whereas one-day initial starvation caused shorter shells and lower percentage of competent larvae. Three days of continuous feeding was required for 50% of the larvae to reach competence. After feeding for 3 days, most larvae could become competent to metamorphose even under starvation. The time of starvation was also critical: larvae that suffered 1-day food deprivation in the first 2 days of larval release had shorter shells and lowered percent competent larvae than those that suffered the same length of food deprivation in later stages of development. Our study thus indicates that both food concentration and short-term starvation have detrimental effects on the larval development of this species, and that once the larva has consumed certain amount of food, starvation may induce metamorphosis.     

Trophic modification of food quality by heterotrophic protists: species-specific effects on copepod egg production and egg hatching

Recent literature suggests that heterotrophic protists could improve the biochemical constituents of poor quality algae for subsequent use by higher trophic levels, a phenomenon dubbed “trophic upgrading”. We conducted experiments to test trophic upgrading effects on the omnivorous calanoid copepod Acartia tonsa. Two heterotrophic protists, Oxyrrhis marina and Gymnodinium dominans, were grown on three algal species of different nutritional qualities: Dunaliella tertiolecta, Isochrysis galbana and Rhodomonas salina. In parallel incubations, the copepods were fed the heterotrophic protists or the algae that the protists grew on. We measured the ingestion rate, egg production rate and egg hatching success of the copepods in each treatment. Comparison of the egg production efficiency (EPE; egg carbon production/carbon ingestion×100%) between parallel diet treatments allowed us to calculate the trophic upgrading index (TUI; ratio of EPE-heterotrophic protist to EPE-alga). The copepods ingested similar amount, or 20-30% more algae than heterotrophic protists. Daily rations ranged 50-122% of body C per day. Copepods feeding on O. marina that grew on D. tertiolecta had higher egg production rate and egg hatching success than copepods feeding on D. tertiolecta directly, and the resultant TUI between the two treatments was 19.7. Similarly, the copepod egg production was improved by G. dominans that grew on D. tertiolecta and the resultant TUI was 23.3. TUI was near 1 between I. galbana treatment and the parallel heterotrophic protist treatments, indicating no or little trophic upgrading effects on the copepod's egg production. However, egg hatching success was significantly lower with G. dominans growing on I. galbana. O. marina that grew on R. salina induced a lower EPE relative to the alga itself, yielding a TUI of less than 1. Biochemical data showed that the heterotrophic protists contained eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) even when they fed on alga that lacked these essential fatty acids, which may explain some of the observed trophic upgrading effects and species-specific differences in our experiments. However, our data also suggested that dietary EPA and DHA could not be the sole factors regulating the copepod's reproductive output, and that egg production and egg hatching appeared to have different nutritional requirements and respond differently to the copepod's diets.     

Egg production of the copepod Acartia bifilosa in two contrasting European estuaries in relation to seston composition

The egg production of the copepod Acartia bifilosa was measured and related to environmental variables and food availability in two estuaries located in the same biogeographic region (Bay of Biscay) but showing very strong differences in abiotic and biotic features: the Gironde estuary (France) and the estuary of Mundaka (Spain). The study was conducted during the spring-summer-autumn period of 1994. Food availability was evaluated by analysing the chlorophyll a (Chl a), the particulate organic carbon (POC) and the easily extractable macromolecular compounds such as proteins, carbohydrates and lipids of the seston. The egg production of copepods was estimated from field incubations with natural water, and phytoplankton feeding of adult females was estimated by means of the gut fluorescence method. The nutritional environment of the Gironde was characterised by high amounts of suspended particulate matter (SPM) with low food value, emphasising the mainly detrital origin of the organic matter (OM). In Mundaka, the higher contribution of phytoplankton to the seston led to marked increases in particulate food value accounting for up to 35% of organic matter. The weight-specific egg production was found to be sharply higher in Mundaka (ranging from 0.2 to 0.63×10⁻³ day⁻¹) than in the Gironde (ranging from 0 to 0.13×10⁻³ day⁻¹), but the seasonal trend of variations was similar, the highest weight-specific egg production rates occurring in early summer and the lowest in autumn in both estuaries. Egg production was not correlated linearly with temperature since maximal egg production occurred at intermediate temperatures. In Mundaka, the egg production showed a significant positive correlation with the chlorophyll and the Chl/SPM and the POC/SPM ratios. This coupled with higher values of algal food availability (Chl a/SPM: 10 to 1870 μg g⁻¹) and gut fluorescence (between 0.12 and 0.38 ng Chl a Eq ind⁻¹) indicate that a herbivorous diet could cover the energy requirements of A. bifilosa and support egg production. In the Gironde, the algal food availability and the gut fluorescence were lower (Chl a/SPM: 10 to 80 μg g⁻¹; GF: 0.09 and 0.25 ng Chl a Eq ind⁻¹), and the egg production showed significant positive correlation with the particulate food value, suggesting that other sources of carbon rather than phytoplankton were responsible for the observed changes in egg production. Results indicate that the particular seston properties of each system may be responsible for the noticeable differences in A. bifilosa fertility among estuaries.     

The variance of incubation temperatures does not affect the phenotype of hatchlings in a colubrid snake, Xenochrophis piscator

It has been documented in some reptiles that fluctuating incubation temperatures influence hatchling traits differently than constant temperatures even when the means are the same between treatments; yet whether the observed effects result from the thermal variance, temperature extremes or both is largely unknown. We incubated eggs of the checkered keelback snake Xenochrophis piscator under one fluctuating (Ft) and three constant (24, 27 and 30 °C) temperatures to examine whether the variance of incubation temperatures plays an important role in influencing the phenotype of hatchlings. The thermal conditions under which eggs were incubated affected a number of hatchling traits (wet mass, SVL, tail length, carcass dry mass, fatbody dry mass and residual yolk dry mass) but not hatching success and the sex ratio of hatchlings. Body sizes were larger in hatchlings from incubation temperatures of 24 and 27 °C compared with the other two treatments. Hatchlings from the four treatments could be divided into two groups: one included hatchlings from the 24 and 27 °C treatments, and the other included hatchlings from the 30 °C and Ft treatments. In the Ft treatment, the thermal variance was not a significant predictor of all examined hatchling traits, and incubation length was not correlated with the thermal variance when holding the thermal mean constant. The results of this study show that the mean rather than the variance of incubation temperatures affects the phenotype of hatchlings.     

Size-related and seasonal patterns of egg collar production in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus held in the laboratory produced egg collars all year round. Egg collar production was greatest during July and August and only occurred in females >8-10 mm shell length. The largest individuals (14-16 mm shell length) had the highest fecundity and ceased egg-laying in late September, whilst 8-14 mm individuals laid egg collars until November. Small females (4-6 mm) grew rapidly during the warmer, summer months (April to August), became sexually mature and began laying egg collars in mid-September. Both the range of egg collar wet weights and the maximum wet weight of an individual egg collar increased with female size class. Temperature strongly affected the length of time between the laying of egg collars and the hatching of larvae (9-10 days at 19-20 °C and 14-15 days at 13-14 °C). A close relationship was also found between egg collar wet weight and the number of veliger larvae released.     

Reproductive costs of the symbiotic hydroid Hydractinia symbiolongicarpus (Buss and Yund) to its host hermit crab Pagurus longicarpus (Say)

Studies on the interaction between the hermit crab Pagurus longicarpus and its symbiotic hydroid Hydractinia symbiolongicarpus have focused on positive effects of hydroids on their host hermit crabs (e.g., protection from predators). Yet, these benefits may be balanced with reproductive costs, which are rarely studied. Results from field observations, laboratory trials, and a mesocosm experiment indicate that female hermit crabs in hydroid-colonized shells exhibit depressed ovigery, smaller clutch sizes, and increased clutch failure relative to females in bare shells. Frequent switching between bare and hydroid-colonized shells may alleviate negative effects when the density of hydroids in the environment is low, but at high densities Hydractinia may significantly impact hermit crab reproduction.     

Mycobiota associated with the ambrosia beetle Scolytodes unipunctatus (Coleoptera: Curculionidae, Scolytinae)

Ambrosia beetles (Coleoptera: Scolytinae) are associated with strictly entomochoric and mutualistic fungi. We studied the mycobiota associated with Scolytodes unipunctatus, ambrosia beetles that infest Cecropia trees in Central America. Isolates were characterized using morphology and rDNA sequences (ITS region, LSU, and SSU rDNA). Four species are described here: Raffaelea scolytodis sp. nov. (Ophiostomatales), Gondwanamyces scolytodis sp. nov., Custingophora cecropiae sp. nov., and Graphium sp. (Microascales). The genus Custingophora is emended to include Knoxdaviesia anamorphs of Gondwanamyces based on uniformity of DNA sequences and phenotype.     

杂色山雀亲代喂食与子代乞食间的行为

在育雏期,晚成鸟的子代一般都是由双亲共同来抚育,子代为了更好地存活,会用自己的方式竞争获得更多的食物和更好的生存空间,同时亲代也会根据子代的乞食信号来分配食物。2011年3～7月采用针孔摄像技术录制了杂色山雀(Parus varius)育雏期巢内亲代与子代间的行为,统计了亲鸟站位、雏鸟站位、雏鸟乞食强度及亲鸟的喂食情况等数据。分析结果表明:(1)雌雄亲鸟在巢中的站位各有特点,雄鸟在整个育雏期都喜欢站在距离巢口较近的位置;雌鸟站位不太固定,前期离巢口相对较远,中期和后期离巢口相对较近;(2)雏鸟离亲鸟越近,乞食强度越大,获得食物的机会就越多;离亲鸟越远的雏鸟越不爱乞食,所以站位对雏鸟的食物获得影响最大;(3)雌鸟承担主要的育雏任务,喂食频率远大于雄鸟;(4)育雏期的不同阶段雏鸟乞食强度、亲鸟喂食频率变化很大:中期雏鸟乞食强度最大,亲鸟喂食频率最高,后期雏鸟乞食强度最弱;(5)整个育雏期雌性亲本没有表现出明显的偏爱行为,但雄性亲本在中、后期更偏爱体型大的雏鸟。可见杂色山雀子代的行为和体型大小影响着亲代的食物分配,亲代也会根据雏鸟日龄调整站位和喂食行为。