The state of populations of <Emphasis Type="Italic">Lernaea cyprinacea</Emphasis> L. (copepoda: lernaeidae) and crucian carp <Emphasis Type="Italic">Carassius carassius</Emphasis> L. in Dlinnoye Lake

The state of populations of the crucian carp Carassius carassius L. and the copepod parasite Lernaea cyprinacea L. was studied after 10 years of a sharp decrease in their abundance. Only one generation of Lernaea cyprinacea species was recorded each year. The alteration of the parasite generation occurred in the second half of July. Changes in the age structure of the copepod population did not affect the distribution pattern of its abundance in the host population, but the values of the K exponent changed in accordance with alterations of the parasite generations. By 2007 the sex ratio in the population became equal, males and females differed in their lengths and weights, and three dimensional groups were found in the catches. It is thought that males and females of the crucian carp have different roles in the maintenance of the L. cyprinacea abundance. The dominating fish sizes and the level of the host infection by copepods remained the same as in 1997–2003.     

Sex-specific response of a mosquito to parasites and crowding

Host-parasite interactions are significantly influenced by the sex of the host and the environment in which the host is found. Sex-specific responses to parasite infection, however, may change according to the host environment. I examine the combined effect of parasite infection and crowding on males and females of the mosquito Aedes albopictus. At a high larval density, infected males experienced a greater relative reduction in body size than did infected females, whereas the pattern was reversed at low density. This experiment demonstrates the importance of the environment on sex-specific responses to parasites and contributes to a growing body of work examining sources of variation in host-parasite interactions.     

Sex‐dependent infection causes nonadditive effects on kissing bug fecundity

The influence of parasites on host reproduction has been widely studied in natural and experimental conditions. Most studies, however, have evaluated the parasite impact on female hosts only, neglecting the contribution of males for host reproduction. This omission is unfortunate as sex‐dependent infection may have important implications for host–parasite associations. Here, we evaluate for the first time the independent and nonindependent effects of gender infection on host reproductive success using the kissing bug Mepraia spinolai and the protozoan Trypanosoma cruzi as model system. We set up four crossing treatments including the following: (1) both genders infected, (2) both genders uninfected, (3) males infected—females uninfected, and (4) males uninfected—females infected, using fecundity measures as response variables. Interactive effects of infection between sexes were prevalent. Uninfected females produced more and heavier eggs when crossed with uninfected than infected males. Uninfected males, in turn, sired more eggs and nymphs when crossed with uninfected than infected females. Unexpectedly, infected males sired more nymphs when crossed with infected than uninfected females. These results can be explained by the effect of parasitism on host body size. As infection reduced size in both genders, infection on one sex only creates body size mismatches and mating constraints that are not present in pairs with the same infection status. Our results indicate the fitness impact of parasitism was contingent on the infection status of genders and mediated by body size. As the fecundity impact of parasitism cannot be estimated independently for each gender, inferences based only on female host infection run the risk of providing biased estimates of parasite‐mediated impact on host reproduction.     

Host-parasite coevolution: comparative evidence for covariation of life history traits in primates and oxyurid parasites.

The environmental factors that drive the evolution of parasite life histories are mostly unknown. Given that hosts provide the principal environmental features parasites have to deal with, and given that these features (such as resource availability and immune responses) are well characterized by the life history of the host, we may expect natural selection to result in covariation between parasite and host life histories. Moreover, some parasites show a high degree of host specificity, and cladistic analyses have shown that host and parasite phylogenies can be highly congruent. These considerations suggest that parasite and host life histories may covary. The central argument in the theory of life history evolution concerns the existence of trade-offs between traits. For parasitic nematodes it has been shown that larger body sizes induce higher fecundity, but this is achieved at the expense of delayed maturity. As high adult mortality would select for reduced age at maturity, the selective benefit of increased fecundity is expressed only if adult mortality is low. Parasite adult mortality may depend on a number of factors, including host longevity. Here we tested the hypothesis concerning the positive covariation between parasite body size (which reflects parasite longevity) and host longevity. To achieve this goal, we used the association between the pinworms (Oxyuridae, Nematoda) and their primate hosts. Oxyurids are highly host specific and are supposed to be involved in a coevolutionary process with their hosts. We found that female parasite body length was positively correlated with host longevity after correcting for phylogeny and host body mass. Conversely, male parasite body length and host longevity were not correlated. These results confirm that host longevity may represent a constraint on the evolution of body size in oxyurids, at least in females. The discrepancy between female and male oxyurids is likely to depend on the particular mode of reproduction of this taxon (haplodiploidy), which should result in weak (or even null) selection pressures to an increase of body size in males.     

Predation risk and feeding patterns of crucian carp

As part of an experimental study of the direct and indirect effects of piscivory on prey fish, the diets of crucian carp Carassius carassius were compared across sections of a divided pond; two sections were stocked with crucian carp alone and two with crucian carp plus perch Perca fluviatilis . Analysis of crucian gut contents indicated that the composition of invertebrate prey did not differ in the presence v . absence of perch. However, crucians, particularly small individuals (<10cm) that were most vulnerable to predation, displayed a lower intake of invertebrate prey in sections with perch. Although diet composition differed between crucians caught in inshore v. offshore habitats (with habitat use being related to crucian size and the presence or absence of perch), no clear pattern existed between habitat and total food intake. Overall, the major effects of predators on the diet of crucian carp appeared to be caused by increased ecological density (resulting from confinement of small crucians inshore) and reduced activity levels, rather than simple shifts to safer habitats.     

How host size may constrain the evolution of parasite body size and clutch size. The parasitic isopod Ichthyoxenus fushanensis and its host fish, Varicorhinus bacbatulus, as an example

The flesh-burrowing parasitic isopod Ichthyoxenus fushanensis was found infecting the body cavity of a freshwater fish, Varicorhinus bacbatulus , in heterosexual pairs. Herein we investigate the question of how the host body size may constrain the parasite size and clutch size by analyzing the interactions among the body size and clutch size of the parasite, and host size. Due to the low transmission rate of I. fushanensis to its host and the positive relationship between clutch size and female size, selection may favor larger females with larger clutch sizes to compensate for massive losses of manca (the free-living juveniles). The path model reveals that clutch size depends not only directly on female size, but also on the sizes of her host and mate. Female size also depends on the sizes of the host and her mate. A negative correlation exists between the body sizes of the paired males and females. This negative correlation may be regarded as a consequence of competition for limited available space or other resources provided by the host. The effects of host size on parasite size, however, act on the total volume of both sexes as a whole, not specifically on either the female or the male. In this case, the available space/resources may not allow both individuals of different sexes to evolve toward a larger size simultaneously. Under the constraint of host size, a strategy of reducing the body size of the paired male may provide a way to increase the body size of the paired female and achieve a larger clutch size.     

Parasites and showy males: malarial infection and color variation in fence lizards

Summary Hamilton and Zuk (1982) proposed that the quality of male showy traits reflects genetically-based resistance to parasites and can be used by females to select mates that are less prone to parasitic attack. The hypothesis requires that a particular state of a variable showy trait should be associated with parasite infection. We tested this idea with a population of western fence lizards, Sceloporus occidentalis, infected with the malarial parasite, Plasmodium mexicanum. Ventral color pattern is strongly dimorphic in fence lizards and varies greatly among males in this population. Malaria-infected males exhibited significantly more black and less pale on their ventral surface than did noninfected males of similar body size. This difference was not a function of differing ages of infected and noninfected animals of the same body size. However, logistic regression demonstrated that females using male ventral color as a gauge of infection status would only marginally improve their chance of choosing a noninfected lizard over random selection of mates.     

Effects of commercial fishing on the population structure of spawning southern calamary (Sepioteuthis australis)

This study explored population dynamics of Sepioteuthis australis on a fine temporal scale before, during, and after a 3-month commercial fishing closure on the summer inshore spawning grounds of Great Oyster Bay, Tasmania, Australia. An abrupt change in male size (mantle length) and population sex ratio after the re-opening of the commercial fishery suggests that fishing alters the population structure on the spawning beds from a ‘natural’ structure which is highly biased towards males, to a more even ratio of males to females. Although jigs are taking a representative sample of the squid population using the spawning beds at any one time, the fishery is apparently still effectively selective for males, potentially as a function of differential spawning movements of the two sexes. Increased fishing pressure over the past 5 years had been correlated with a change towards a highly male-biased sex ratio on the spawning beds; however the current study suggests that increased fishing pressure in recent years may not have reduced the proportion of females. Instead, the inter-annual change in sex ratio may reflect changes in the degree of protection from fishing, with progressively longer closures allowing time for more males to accumulate on the beds and therefore, for the proportion of males to increase (as opposed to a decrease of females). As fishing is selective for males, fishing throughout the spawning season could potentially modify the process of sexual selection and the mating behaviors of the individuals within the spawning population, highlighting the need for closures over this crucial period. Additionally, examinations and comparisons of squid population structure need to be interpreted in light of fishing pressure and broader movement patterns.     

瓯江口凤鲚生长、死亡和最适开捕体长

根据2015、2018—2020年瓯江口水域渔业资源监测调查资料, 对1359尾凤鲚的体长、全长和体重等生物学信息进行测定, 利用体长频率分布估算凤鲚种群生长、死亡参数等。结果表明, 瓯江口凤鲚体长为5.2—21.9 cm; 体长和体重的关系式W=0.0035×L_3.0783。用ELEFAN技术拟合的von Bertalanffy生长方程的各参数为L_∞=26.60 cm, k=0.47及t₀=–0.55 a; Z=2.30, M=1.00, F=1.30, E=0.567, 表明资源处于过度开发状态; 凤鲚的首次捕捞体长L_c=15.35 cm, 对应首次捕捞平均年龄为1.28 a, 小于临界年龄(1.36 a)和体重生长的拐点年龄(1.85 a),表明当前渔业主要捕捞对象为幼鱼和补充群体, 无法保证资源的有效补充。在瓯江口凤鲚目前的资源状态下, 应努力降低捕捞死亡率, 并加强对凤鲚栖息环境的保护, 而对目前以小型化和低龄化为主的凤鲚群体, 以控制开捕体长为主, 根据Beverton-Holt动态模型...     

The role of host sex in parasite dynamics: field experiments on the yellow-necked mouse Apodemus flavicollis

We investigated the role of host sex in parasite transmission and questioned: ‘Is host sex important in influencing the dynamics of infection in free living animal populations?’ We experimentally reduced the helminth community of either males or females in a yellow‐necked mice (Apodemus flavicollis) population using an anthelmintic, in replicated trapping areas, and subsequently monitored the prevalence and intensity of macroparasites in the untreated sex. We focussed on the dominant parasite Heligmosomoides polygyrus and found that reducing parasites in males caused a consistent reduction of parasitic intensity in females, estimated through faecal egg counts, but the removal of parasites in females had no significant influence on the parasites in males. This finding suggests that males are responsible for driving the parasite infection in the host population and females may play a relatively trivial role. The possible mechanisms promoting such patterns are discussed.     

Epizootiology of blood parasites in an Australian lizard: a mark-recapture study of a natural population

The dynamics of a naturally endemic blood parasite (Hepatozoon hinuliae) were studied in a lizard (Eulamprus quoyii) host population, using 2 years of longitudinal data. We investigated how parasite abundance in the population varied over time, examined whether certain host sub-populations were more prone to infection, and compared parasite loads in relation to host reproductive behaviour. We recorded blood parasite infections of 331 individuals, obtained in 593 captures. Prevalence (the proportion of the host population infected) of blood parasites was high; approximately 66% of the lizard population was infected. Probability of infection increased with host age and size, but did not differ between the sexes. Within individuals, parasite load (the intensity of infection within individuals) did not vary over time, and was independent of host reproductive behaviour. Parasite load was significantly higher in males compared to females.     

Mediterranean Diplodus annularis (Teleostei: Sparidae) and its brain parasite: unforeseen outcome

Patterns of parasite load and aggregation of the bird trematode Cardiocephaloides longicollis in its main intermediate host in the Mediterranean, the annular sea bream, Diplodus annularis, were studied in a large sample collected off Valencia (Spain) and are discussed within the context of the parasite induced host mortality hypothesis. The metacercariae were located within large composite cysts of host origin in the ventricles of the optic lobes of the cerebrum. A weak immunological response was detected in older fish, which was significantly associated with the total parasite load. Although the mean abundance of C. longicollis showed a tendency to increase with host size, the infection levels were generally homogeneous with a noticeable plateauing in the intermediate size classes. The distribution of the metacercariae was aggregated and agreed with the negative binomial distribution. There was a marked decline in parasite aggregation in the largest size-class, suggesting parasite-induced host mortality in the oldest fish possibly due to predation by large non-host fish predators. On the other hand, levelling off of abundance and decrease in heterogeneity of parasite distribution within the intermediate age cohort could indicate that these sizes are being rapidly and/or constantly removed from the host population due to by-catch fishing. The overall high infection levels and the continuous recruitment across age cohorts provides evidence that an enhanced parasite transmission is taking place in the Gulf of Valencia due to increased spatial overlap of the hosts involved in the life cycle. We suggest a human-induced facilitation of the digenean life cycle due to the fact that gulls in the area feed extensively on discards, thus indicating the possibility of an unforeseen effect of fishing practices in a marine littoral system.     

Female-biased operational sex ratio of sexual host fish in a gynogenetic complex of Carassius auratus

To study the coexistence of sexual and gynogenetic forms, we examined the population structure of a gynogenetic complex of the Japanese crucian carp, Carassius auratus Temminck et Schlegel, during the April–June reproductive season by collecting 1225 mature fish that migrated from Lake Suwa to a tributary river for spawning. There were more sexual fish (about 80%) than gynogenetic fish in this complex, and the operational sex ratio in the sexual form was female biased (males were about 20%). Mean standard length and body weight of sexual females were larger than those of sexual males. Sex ratio was male biased in smaller fish (standard length, <8.5 cm) but female biased in larger fish (standard length, ≥8.5 cm). We determined age by scale ring marks; the average age of sexual females was higher than that of males, but there was no significant difference in the average age between sexual and gynogenetic females. Sex ratio in the sexual form was more female biased for old than for young fish, and the mean size of sexual females was larger than that of males of the same age. The clear female-biased sex ratio and age difference between sexual females and males can be explained either by (1) higher mortality of males or by (2) female-biased sex allocation. The latter process reduces the disadvantage of sex and contributes to the coexistence of sexual and gynogenetic forms. Received: November 24, 2000 / Accepted: March 6, 2001     

Female-biased infection and transmission of the gastrointestinal nematode Trichuris arvicolae infecting the common vole, Microtus arvalis

Previous studies addressing the importance of host gender in parasite transmission have shed light on males as the more important hosts, with the higher transmission potential of males being explained by the fact that they often harbour higher parasite loads than females. However, in some systems females are more heavily infected than males and may be responsible for driving infection under such circumstances. Using a wild population of common voles (Microtus arvalis), we showed that females were more frequently infected by the intestinal nematode Trichuris arvicolae than males (i.e. prevalence based on the presence of eggs in the faeces) and that females were shedding greater numbers of parasite eggs per gram of faeces (EPG) than males. By applying an anthelmintic treatment to either male or female voles, we demonstrated that treating females significantly reduced parasite burdens (i.e. prevalence and EPG) of both male and female hosts, while treating males only reduced parasite burden in males. These findings indicate that in this female-biased infection system females play a more important role than males in driving the dynamics of parasite transmission.     

POSITIVE GENETIC CORRELATION BETWEEN PARASITE RESISTANCE AND BODY SIZE IN A FREE-LIVING UNGULATE POPULATION

Abstract Parasite resistance and body size are subject to directional natural selection in a population of feral Soay sheep (Ovis aries) on the island of St. Kilda, Scotland. Classical evolutionary theory predicts that directional selection should erode additive genetic variation and favor the maintenance of alleles that have negative pleiotropic effects on other traits associated with fitness. Contrary to these predictions, in this study we show that there is considerable additive genetic variation for both parasite resistance, measured as fecal egg count (FEC), and body size, measured as weight and hindleg length, and that there are positive genetic correlations between parasite resistance and body size in both sexes. Body size traits had higher heritabilities than parasite resistance. This was not due to low levels of additive genetic variation for parasite resistance, but was a consequence of high levels of residual variance in FEC. Measured as coefficients of variation, levels of additive genetic variation for FEC were actually higher than for weight or hindleg length. High levels of additive genetic variation for parasite resistance may be maintained by a number of mechanisms including high mutational input, balancing selection, antagonistic pleiotropy, and host‐parasite coevolution. The positive genetic correlation between parasite resistance and body size, a trait also subject to sexual selection in males, suggests that parasite resistance and growth are not traded off in Soay sheep, but rather that genetically resistant individuals also experience superior growth.     

长江丽棘虫种群生态的研究

长江丽棘虫（ＢｒｅｎｔｉｓｅｎｔｉｓｙａｎｇｔｚｅｎｓｉｓＹｕｅｔＷｕ,）隶于棘吻目,长棘吻科,是余仪,伍惠生在长江中游的鱼中采获并定为新种［１］。据他们调查,长江中游有１４种经济鱼类是该种棘头虫的终末宿主,黄颡鱼是终末宿主之一。有关这种寄生蠕虫的种群生物学研究尚未见到报道。１　材料和方法从１９９８年６月至７月中旬,随机购得渔民在江边捕获的黄颡鱼７６尾。在实验室内逐一测量黄颡鱼的全长、体长,称其重量,剖开鱼腹,完整地取出消化道,称鱼的空壳重,逐一解剖检查鱼的胃和肠道,记录检出的寄生蠕虫数量和寄生…     

Changes in size composition of the catches of toothfish Dissostichus eleginoides as a result of longterm long-line fishing in the region of South Georgia and Shag Rocks

The changes in the size composition of the toothfish Dissostichus eleginoides from the long-line catches in division 48.3 (South Georgia and Shag Rocks) and determination of the length at which the males and females mature are investigated, as is the ratio between the mature and immature individuals of this species after the longterm effect of fishing. It was shown that toothfish males reach maturity at smaller lengths than females. Fifty percent of males reach maturity at length of 66–78 cm, while females mature at lengths of 78–96 cm. The ogive of toothfish maturation and its comparison with size and sexual composition of the catches in the first and last years of long-line fishing demonstrated that a significant part of immature and first maturating fishes less than 90 cm in length are removed as the result of fishing at the present time. The decrease in the average size of toothfish in the catches, the high percent of immature fishes in the catches, and the decrease of the portion of large fishes suggest a decrease in its abundance.     

Reproductive success, mortality and sexual size dimorphism in the adder, Vipera berus

From 1981 to 1986 an isolated adder population was studied in the extreme south of Sweden. During this period 48 adult males and 44 adult females were marked. Male adders did not grow as large as the females. Large males had a significantly higher annual mating success and were engaged in more combats than smaller males. The mean length of recaptured males was significantly lower than that of those not recaptured, indicating a higher motality of larger males. Females brood size was positively correlated with body size. In females there was no difference in mean length of recaptured vs not recaptured individuals. The adder is one of the few snake species with male combat where males are smaller than females. I suggest that this is due to stronger selective advantages for large body size in females than in males.     

Comparative characteristic of sablefish Anoplopoma fimbria in catches with passive and active fishing gear in the northwestern Pacific ocean

According to materials of trap, long-line, and trawl fishing, specific features of distribution of sablefish Anoplopoma fimbria and some of its biological characteristics in Pacific waters off the southeastern coast of Kamchatka, continental slope of the western part of the Bering Sea, Shirshov Underwater Ridge, and off the Commander Islands are considered. Maximum density concentrations according to data of trap fishing was noted along southeastern coast of Kamchatka and the data of trawl fishing indicated most frequent catches in the western part of the Bering Sea in the area of Koryak coast up to Cape Navarin. The pattern of vertical distribution in different areas considerably differs. The magnitude of trap catches in different areas is different and determined by the type of trap and the period of soaking. The size composition, fatness, and the sex ratio are different in catches of different fishing gear and differ between regions. On the whole, in Russian Far Eastern waters, females mature in mass at a body length of 71 cm and males at 57 cm.     

Hyperparasitism of the cryptoniscid isopod Liriopsis pygmaea on the lithodid Paralomis granulosa from the Beagle Channel, Argentina

A total of 29,570 false king crab Paralomis granulosa were sampled from the Beagle Channel (54 degrees 51'S, 68 degrees 12'W), Tierra del Fuego, Argentina, between July 1996 and August 1998. Crab size varied from 6.8 to 111.2 mm carapace length (CL). A few crabs parasitized by the rhizocephalan Briarosaccus callosus were found; prevalences of externae (the rhizocephalan reproductive body) and scars (the mark left on the host after the death of the parasite) were 0.28 and 0.16%, respectively. Of 85 externae examined, 55 were non-ovigerous and 30 ovigerous. The cryptoniscid isopod Liriopsis pygmaea infested 36.5% of the B. callosus examined. The most abundant stage was the cryptonicus larva, accounting for 208 of the 238 L. pygmaea recovered. Cryptonisci showed a highly aggregated distribution. A total of 92.7% of cryptonicsci were recovered inside empty externae, suggesting that the latter were attractive to cryptonisci. Early subadult females of L. pygmaea were rare; only 3 individuals occurred inside 1 ovigerous externa. Eight late subadult and 18 adult females were found on 3 and 7 non-ovigerous externae, respectively; in addition, 1 aberrant late subadult was found on 1 ovigerous externa. In the Beagle Channel, the population of P. granulosa harbours 3 different parasites: the bopyrid isopod Pseudione tuberculata, which reaches highest prevalence at 10 to 20 mm CL, the rhizocephalan B. callosus, with highest prevalence at 20 to 40 mm CL, and the cryptoniscid isopod L. pygmaea, which mainly infests rhizocephalan on crabs >40 mm CL.