Non-reproductive Periods Research Articles

Host selection and influencing factors of parasitic fleas on the body surface of desert rodents, Inner Mongolia, China

Fleas frequently parasitize rodents and serve as major vectors for many zoonotic diseases. The Alxa Desert in Inner Mongolia, China, is a typical arid region in Asia, which is suitable for the coexistence of a variety of rodents in this environment. Understanding the host selection of fleas among these rodents and the factors influencing this selection is crucial for comprehending rodent-borne diseases and the vector roles of fleas. This study utilized live-trap methods to capture rodents coexisting in the Alxa Desert from April to October 2022. Body surface fleas were collected and analyzed for abundance across different hosts, sexes, and reproductive statuses. The results indicated that: (1) there were significant differences in the species and abundance of parasitic fleas on different rodent species, with Ophthalmopsylla kiritschenkoi and Mesopsylla hebes preferring the Dipus sagitta and Orientallactaga sibirica as their hosts, and Xenopsylla conformis preferring Meriones meridianus as its host. (2) Fleas exhibited sex-preferential host selection, showing a greater preference for male hosts. (3) Among rodents of different reproductive states, most fleas prefer to parasitize individuals in non-reproductive periods. (4) The mean abundance of fleas varied significantly between seasons (P < 0.05), with spring and autumn being the peak periods for flea parasitism. (5) Factors influencing the mean abundance of fleas included host species, sex, reproductive status, and season, with host species having the greatest impact.

Links between reproduction and immunity in two sympatric wild marine fishes

According to life-history theory, limited resources can result in trade-offs between costly physiological functions. Particularly, it can be expected that individuals present lower immune function, or an alternative immunological strategy, during their reproductive compared to their non-reproductive season. Here we investigate the link between reproduction and immunity in two sympatric marine fish species, the rockfish Sebastes oculatus and the sandperch Pinguipes brasilianus. The results showed lower values of total white blood cells and spleen index, but higher levels of natural antibodies (only in females) in reproductive rockfish compared to non-reproductive ones. On the other hand, reproductively active sandperch showed lower levels of natural antibodies and a higher neutrophil to lymphocyte ratio and spleen index (only in males), compared to non-reproductive ones. Also, negative correlations between reproductive and immune parameters were observed in female rockfish at the individual level, but not in sandperch. Our results are consistent with the presence of different immunological strategies in reproductive and non-reproductive periods, with patterns that appear to be species-specific. This specificity suggests that various aspects of immunity might respond differentially to resource limitation, which could be associated with the disparate life-history strategies of the studied species. Alternatively, though not exclusively, the observed patterns could be driven by abiotic factors that characterize the reproductive season of each species (i.e., winter for rockfish, summer for sandperch). Our study contributes to ecoimmunological knowledge on free-living fish and highlights that detection of trade-offs can depend on the combination of study species, season, sex, and specific immune components measured.

Feeding habits of South American and sub‐Antarctic fur seals during their nonbreeding season in the southwestern Atlantic Ocean

AbstractStomach contents of South American (Arctocephalus australis) (n = 219) (SAFS) and sub‐Antarctic (A. tropicalis) (n = 37) (SFS) fur seals were opportunistically sampled from 1980 to 2021 to examine their feeding habits and resource partitioning in southern Brazil while in their nonreproductive periods. SAFSs mainly consumed abundant coastal pelagic species, such as Anchoa marinii and Doryteuthis sanpaulensis, resulting in high sexual trophic niche overlap. The frequency of occurrence (%FO) of fish prey, especially the overexploited Micropogonias furnieri, decreased between 1980–1992 and 2007–2021, while squid increased. For SFSs, offshore squids such as Ommastrephes bartramii and Illex argentinus were the most important prey considering both sexes in the long‐term. The interspecific trophic niche overlap was low, but it is likely underestimated since it increased with the inclusion of scat samples from SFSs. This sample‐size effect was also observed in Shannon's diversity index, which was lower for underrepresented SFSs. Marine debris ingestion was detected in both species (SAFS %FO = 2.7; SFS %FO = 8.3), with only flexible plastic material found. This study brings novel information on feeding habits of fur seal species in the extreme south of Brazil, as well as unprecedented information about their ecology during the nonreproductive period.

Cellular Modifications in Spermatogenesis during Seasonal Testicular Regression: An Update Review in Mammals.

Simple SummaryThe most common form of reproduction in mammals is seasonal reproduction. This ensures that offspring are born at the most suitable time for survival, due to the abundance of food and the optimal temperatures for early postnatal development. In males, one way to achieve this is to decrease or lose fertility over a given period. This loss is associated with a greater or lesser degree of spermatogenesis modification that affects both germ and Sertoli cells. This paper reviews the different cellular mechanisms that have been postulated in recent years to explain how the activity of the seminiferous epithelium decreases during the non-reproductive period.Testicular regression occurs during the non-breeding season in many mammals. This affects spermatogenesis, resulting in decreased or arrested activity. Both lead to a decrease or cessation in sperm production. In recent years, the cellular mechanisms that lead to infertility in males in non-reproductive periods have been studied in very different species of mammals. At the start of the present century, the main mechanism involved was considered as an increase in the apoptotic activity of germ cells during the regression period. The loss of spermatogonia and spermatocytes causes not only a decrease in spermatogenesis, but an arrest of the seminiferous epithelium activity at the end of regression. Recently, in some mammal species, it was found that apoptosis is the usual mechanism involved in epithelium activity arrest, although it is firstly atrophied by massive desquamation of the germ cells that are released from their binding with the Sertoli cells, and which are shed into the lumen of the seminiferous tubule. In other species, it has been shown that not only germ cell apoptosis, but also Sertoli cell apoptosis, including decreased proliferative activity, spermatophagy or autophagy, are involved in testicular regression. Furthermore, the most recent studies indicate that there are multiple patterns of seminiferous epithelium regression in seasonally breeding animals, which may not only be used by different species, but also by the same ones to reproduce in the best conditions, ensuring their survival. In conclusion, at this time, it is not possible to consider the existence of a paradigmatic cellular mechanism in the involution of the seminiferous epithelium applicable to all male mammals with seasonal reproduction, rather the existence of several mechanisms which participate to a greater or lesser extent in each of the species that have been studied to date.

An autofluorescence-based survey of late follicular atresia in ovaries of a teleost fish (Thunnus thynnus).

In this study, the authors examined late atretic follicles in the ovaries of Atlantic bluefin tuna, Thunnus thynnus (Linnaeus 1758), at different times of the year using transmitted light and epifluorescence microscopy. Atresia (degeneration and resorption of developing ovarian follicles) is a natural process involved in fecundity downregulation in teleosts and is substantially enhanced in stressful conditions. Early (α and β) atretic stages of yolked oocytes have a relatively short duration in seasonally reproducing species, whereas later (γ and δ) atretic follicles (LAF) persist for longer time in the ovary, serving as a sign of previous vitellogenic activity. LAF can thus be used as reliable markers of maturity during non-reproductive periods. Lipofuscin granules accumulate in the cytoplasm of LAF cells as a result of lysosomal digestion of oocyte components. Taking advantage of the well-known autofluorescent properties of lipofuscins, LAF may be identified in unstained histological sections under fluorescence microscopy using appropriate excitation and emission wavelengths. The authors explore in this study the applicability of fluorescence microscopy to provide a fast and effective method to assess late atresia in fishes. This method may be particularly useful to determine sexual maturity in individuals sampled long after the spawning season, where LAF are difficult to detect in standard histological sections. Furthermore, LAF autofluorescence provides a rapid way to quantify late atresia in fishes using image analysis.

Health Services, Socioeconomic Indicators, and Primary Care Coverage in Mortality by Lower Genital Tract and Breast Neoplasias in Brazilian Women during Reproductive and Non-Reproductive Periods.

Women’s health assistance at the low-complexity level is focused on the most common diseases and can be affected by primary health care coverage, particularly in areas far away from large urban centers. Thus, in this work, we aim to analyze the relationship between socioeconomic status, health care indicators, and primary care coverage in mortality from neoplasms of the lower genital tract and breast in Brazilian women during reproductive and non-reproductive periods. We conducted an ecological study at the Gynecology Discipline, Medicine School, University of São Paulo. Secondary data were collected from women according to reproductive periods and mortality data from the Mortality Information System based on International Classification of Disease—10th edition regarding breast and lower genital tract neoplasms in 2017. The health service and socioeconomic indicators were obtained from the Informatics Department of the Unified Health System and Brazilian Institute of Geography and Statistics. Our results showed that primary care coverage and health service indicators were not associated with mortality from breast cancer and the female lower genital tract, both in reproductive and non-reproductive periods. Sociodemographic indicators were found to be associated with mortality from breast cancer and the female lower genital tract, with income being associated with reproductive period (β = −0.4; 95% CI, −0.8 to −0.03) and educational level in the non-reproductive period (β = 9.7; 95% CI, 1.5 to 18.0).

Residency and dispersal of three sportfish species from a coastal marine reserve: Insights from a regional-scale acoustic telemetry network

Understanding the movements of adult fish around marine reserves is central to evaluating the importance of these areas to conservation but is difficult to quantify in many coastal settings. We used a 300 km long passive acoustic telemetry network to measure site fidelity and dispersal distances of adult red drum (Sciaenops ocellatus), black drum (Pogonias cromis), and spotted seatrout (Cynoscion nebulosus) tagged within two estuarine no-take zones at Kennedy Space Center, Florida, USA. Seventy-eight tagged fish were tracked an average of 549 days with some individuals followed for over four years. Fish spent most of their total time at liberty inside no-take zones with a mean residency of 125–178 consecutive days after release, and 67%–95% of their total time, depending on species. Sixty-four individuals (82%) also utilized adjacent public waters, dispersing up to 650 km, although dispersal rates averaged less than 0.10 km day−1 for all three species. Red drum and black drum movements across reserve boundaries were clearly bi-directional with individuals averaging 4 and 30 excursions per year, respectively, into fished areas. Both species spent more time outside reserve boundaries during their reproductive periods, suggesting that these no-take zones protect individuals that subsequently spawn over a wider geographic area. Our findings demonstrate that coastal marine reserves have the potential to provide substantial protection for highly mobile non-reef fishes. They further suggest that reserves designed to safeguard fish during non-reproductive periods may be most practical for estuarine species whose home ranges increase during spawning seasons.

Evaluation of the quality of life of women in the climacteric attended by the basic care of the municipality of Sinop-MT

The World Health Organization (WHO) defines climacteric as a biological phase of life and not a pathological process, which refers to the transition between the reproductive and non-reproductive periods of women's lives. The objective of this study was to evaluate the quality of life of climacteric women attended by the Carlos Scholtão Family Health Units and Jardim Botânico. This is a quantitative study, in which 41 women were evaluated, with symptoms related to the climacteric, age from 40 to 65 years, without hormonal therapy. To collect data, two questionnaires were applied, first one with questions related to socio-demographic data, health status and life habits, and to collect data on women's health, the Women's Health Questionnaire (QSM), developed and validated by Hunter in 1992. Through the study it was demonstrated that the climacteric symptoms did not significantly interfere in the quality of life of the women surveyed. It was also observed that even without reported symptoms, many reported using antidepressant medications, which may interfere with the intensity of the climacteric symptomatology. Research has shown to be different from most studies that deal with women's quality of life in the climacteric, which reinforces the importance of local studies with different approaches. Through the research the interest was aroused by the self-knowledge in the participants and evidenced that the nursing has an important role in the incentive of self-care. At the end of the research it was observed that some women had difficulty understanding the questionnaires, which suggests the application of other methodologies in future studies.

Reproduction in the Eared Dove: An exception to the classic model of seasonal reproduction in birds?

In avian species living at high altitudes and latitudes, reproductive events are largely controlled by photoperiod, with changes being perceived mainly through encephalic photoreceptors located in the hypothalamus. It is known that during long day periods (reproductive periods), the information transmitted by brain photoreceptors triggers the production of thyroid hormones that regulate GnRH secretion, inducing secretion of pituitary gonadotropins. As a result, gonads develop and grow and the production of gonadal sex hormones, testosterone and estradiol increases (classic gonadal cycle). During short day periods (non-reproductive periods) on the other hand, the gonads regress, and plasma gonadal steroid levels are low. By means of this mechanism, birds synchronize their physiology and reproductive behaviors with seasonal changes in the environment. However, it appears that not all avian species comply with this general reproductive pattern. For example, the Eared Dove (Zenaida auriculata), a South American opportunistic breeding columbiform, has been reported to successfully reproduce throughout the year, making it an interesting avian system for studying the endocrine basis of avian reproduction. In view of a clear lack of seasonal variability in testicular weight and size (the classic gonadal regression/recrudescence cycle) in the male Eared Dove, we examined whether their reproductive aseasonality could be the result of being in a continuous state of reproductive preparedness. Our results show that despite the absence of a marked gonadal cycle in terms of gonadal volume, plasma testosterone levels in males were minimal during autumn-winter, reaching maximum values during spring-summer. This indicates that male gonad function is not seasonal in terms of spermatogenesis but that circulating testosterone levels are correlated with photoperiod, demonstrating an exception to the classic model of reproduction in birds.

Genetic evidences of non-reproductive shoaling in the freshwater fish Salminus brasiliensis

Recent studies have identified patterns of genetic organization during schooling in the reproductive period of several Neotropical freshwater migratory fish. However, population segregation during non-reproductive periods is still unknown for most species. In this study, we investigated the genetic structure of populations of Salminus brasiliensis, a high-value large migratory freshwater fish, sampled during the non-reproductive season. We analysed 89 adults from Uruguay River Basin (Brazil) collected during the two consecutive non-reproductive periods, and assessed the genetic diversity levels using eleven microsatellite loci. Our results showed that populations are genetically structured, suggesting these fish can remain grouped likely due to a cooperative behaviour, not related to reproduction, in a typical shoaling behaviour. Besides, we found high genetic diversity for S. brasiliensis from the Turvo State Park area, highlighting the importance of this conservation unit as a relevant area for maintaining the genetic variability of S. brasiliensis in the Uruguay River.

Seasonal abundance, vertical distribution and life history traits of Mediterranean mud shrimp Upogebia pusilla (Decapoda: Gebiidea) on the Slovenian coast

We studied seasonal abundance, vertical distribution and life history traits of the Mediterranean mud shrimp (Upogebia pusilla) in the mediolittoral zone in Slovenia. At two localities (Strunjan and Lazaret), quantitative samples from three plots (1 m2 each) at (0 cm), below (-50 cm) and above (+50 cm) mean water level were taken once every two months, in alternation. A set of parameters was also recorded, including vegetation cover, sediment type, air and sea temperature, pH, salinity and oxygen levels. Highest abundance was recorded during the warm period of the year, with peak abundance in June 2012 (21 % of total sample). Lowest plots were always occupied with the highest densities of mud shrimps. Males dominated during the winter while ovigerous females reached the peak in June (&amp;gt;40 % of all animals). In June at least 2/3 of females were ovigerous. Estimated mean incubation period was 31 days. We determined four periods in relation to the species’ reproductive activity. Early reproductive period (April) was characterised by emergence of first ovigerous females, while main reproductive period (May–July) was characterised by peak of reproduction. In post-reproductive (August–October), and non-reproductive (November–March) periods, no ovigerous females or newly hatched offspring were recorded.

Putative drivers of adrenocortical activity in captive African lesser bushbaby (Galago moholi)

In seasonal breeders, periods of reproductive activity often coincide with high levels of glucocorticoids. We studied seven male and seven female African lesser bushbabies (Galago moholi A. Smith, 1836) over two mating periods via noninvasive faecal hormone metabolite monitoring to investigate the relationship between reproductive and adrenocortical hormone activity. We used linear mixed-effect models to investigate the effect of physiological (endocrine) variables on faecal glucocorticoid metabolite concentrations. Our results indicate faecal androgen (males) and progestagen metabolite (females) concentrations as the variables best able to explain variability in faecal glucocorticoid metabolite concentrations. However, the models explained only a fraction (26% and 12%, respectively) of the observed variability and graphical analysis suggests a biologically relevant difference in faecal glucocorticoid metabolite concentrations between captive and free-ranging animals during nonreproductive periods. Thus, captivity may have affected glucocorticoid output in our focal animals, potentially weakening the expected relationship between reproductive activity and faecal glucocorticoid metabolite variability. Due to the ease of faecal and observational sample collection, a large number of studies monitoring adrenocortical activity in wildlife are conducted using only captive settings, with inferences unquestioned when applied to free-ranging scenarios. Our study cautions against this practice, as particular housing or management conditions may influence the pattern of adrenocortical activity.

Long-term-stability of relationship structure in family groups of common marmosets, and its link to proactive prosociality

Cooperatively breeding, group-living common marmosets show differentiated relationships, where more strongly bonded dyads within a group engage more in affiliative interactions than less strongly bonded ones. Intriguingly, recent results suggest that strong bonds do not only occur between breeding partners but between individuals from any sex or status, and that strong-bond partners exhibit correlated oxytocin fluctuations (dyadic oxytocin synchrony, OTS) over a period of six weeks. To date, it is unclear whether such relationships are stable over time and whether they are also reflected in higher partner-specific proactive prosociality. To assess the long-term stability of the relationship structure of common marmoset family groups, we investigated whether hormonal and behavioral markers of group structure (dyadic OTS, dyadic affiliation, and individual group integration) in common marmoset families remained stable over a period of six months. We collected baseline urinary OT and social behavior of 36 dyads from three family groups in a non-reproductive period (period A), and again six months later, around the birth of new infants (period B). Patterns of dyadic OTS, dyadic affiliation, and individual group integration were consistent between the two study periods. Oxytocin data from a fourth group (10 dyads), collected in two non-reproductive periods separated by a period of more than five years, could replicate this finding. Furthermore, OTS was also correlated with proactive prosociality that was assessed experimentally for 38 dyads during an earlier study. These results suggest that differentiated relationships are stable over time, even between group members other than the breeding pair, and that more strongly bonded partners also show higher levels of proactive prosociality. Future studies are necessary to identify whether these relationships have an adaptive function, perhaps with regard to positive consequences on cooperativeness.

Not all crabs are created equal: diverse evolutionary paths of female preferences for courtship structures in fiddler crabs (genus Uca)

ᅟMales of fiddler crabs (genus: Uca) construct courtship structures using mud or sand to attract mate-searching females for underground mating. A sensory trap hypothesis proposes that the courtship structures have evolved by trapping the sensory bias for any objects which the crab approach to evade predators. We tested if the sensory bias commonly exists in three species of fiddler crabs and the outgroup Ocypode stimpsoni, by placing crabs individually at the center of an arena, from which they could choose between burrows with and without structures. Contrary to previous results in other species, male U. lactea showed no orientation response toward holes with or without semidomes. Female U. lactea predominantly visited holes with semidomes during reproductive periods but did not show the response during non-reproductive periods. In contrast, female U. arcuata and male U. terpsichores and even the outgroup female O. stimpsoni showed a strong orientation response to an artificial structure. By inferring the evolutionary history of sensory biases and courtship structures, we conclude that the preference for the courtship structures evolved before the genus Uca branched out from the common ancestor of genus Uca and Ocypode and yet that the sensory bias has been modified or lost in U. lactea. We tested the sensory trap hypothesis for preference for courtship structures in three species of fiddler crabs in different locations and the outgroup O. stimpsoni. Contrary to previous results in other species, one species which build courtship structures (U. lactea) showed sex- and context-dependent orientation responses in the non-courtship context. On the other hand, the other species tested had a strong orientation response to structures. This is the first comparative study supporting that the preference for the courtship structures in fiddler crabs could have different evolutionary paths.

Geographic Variation in Daily Temporal Activity Patterns of a Neotropical Marsupial (Gracilinanus agilis).

The temporal activity of animals is an outcome of both biotic and abiotic factors, which may vary along the geographic range of the species. Therefore, studies conducted with a species in different localities with distinct features could elucidate how animals deal with such factors. In this study, we used live traps equipped with timing devices to investigate the temporal activity patterns of the didelphid Gracilinanus agilis in two dry-woodland areas of the Brazilian savanna (Cerrado). These areas were located about 660 km apart, one in Central Brazil and the other in Southeastern Brazil. We compared such patterns considering both reproductive and non-reproductive periods, and how it varies as a function of temperature on a seasonal basis. In Central Brazil, we found a constant, and temperature-independent activity during the night in both reproductive and non-reproductive periods. On the other hand, in Southeastern Brazil, we detected a constant activity during the reproductive period, but in the non-reproductive period G. agilis presented a peak of activity between two and four hours after sunset. Moreover, in this latter we found a relation between temporal activity and temperature during the autumn and spring. These differences in temporal activity between areas, observed during the non-reproductive period, might be associated with the higher seasonal variability in temperature, and lower mean temperatures in the Southeastern site in comparison to the Central one. In Southeastern Brazil, the decrease in temperature during the non-reproductive season possibly forced G. agilis to be active only at certain hours of the night. However, likely due to the reproductive activities (intensive foraging and searching for mates) this marsupial showed constant, temperature-independent activity during the night in the reproductive period at both sites.

The high cost of reproduction in sea otters necessitates unique physiological adaptations.

Superimposed on inherently high basal metabolic demands, the additional energetic requirements of reproduction can push female sea otters beyond physiological limits. Indeed, the resulting energy imbalance contributes to disproportionately high rates of mortality at the end of lactation in this species. To examine and quantify metabolic changes associated with reproduction, we measured the resting metabolic rate (RMR) of a female sea otter across gestation, lactation and non-reproductive periods. Concurrently, measurements were made on a non-breeding control female. Our results suggest that RMR declines during gestation. Conversely, RMR increases during lactation, reaches a peak at 3-4 months postpartum, and remains elevated until weaning. Combining these direct measurements with published data, we found the cost of pup rearing to be significantly higher than previously estimated. High baseline energy demands and limited energy reserves, combined with significant lactation and pup rearing costs, appear to necessitate metabolic and thermal lability during key reproductive stages.

Polygamous mating system and protogynous sex change in the gobiid fish Fusigobius neophytus

Whereas mating behaviors and social structure have been studied extensively in monogamous hermaphroditic gobiid species, such studies are relatively limited for polygamous gobiid species. To investigate the reproductive strategy of polygamous gobies, mating groups of the common fusegoby Fusigobius neophytus were observed on reefs of Kuchierabu-jima Island, southern Japan. Males established mating nests on flat-rock surfaces within their territorial home ranges on sandy rubble flats. Females maintained independent home ranges outside the male home ranges during nonreproductive periods, but they shifted their home ranges to overlap with male ranges and actively visited male mating nests during their reproductive periods (1–3 days at ca. 7-day intervals). Females often changed mates during their serial mating. The mating system used by the common fusegoby fits with the definition of male-territory-visiting polygamy. The sex ratio within the study population was female-biased. Nest-holding males were significantly larger than females and were polygynous (mating with up to eight females). These characteristics fit well with the prediction of protogyny by the size-advantage model. Some of the females were observed to undergo functional sex changes to nest-holding males. In addition, small floating males demonstrated sneaking behavior. None of the floating males were derived from females that had changed sex, suggesting a diandric life-history pathway for F. neophytus.

Temporal plasticity in thermal‐habitat selection of burbot Lota lota a diel‐migrating winter‐specialist

In this study, animal-borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter-specialist diel-migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12-14° C) optimal for hunting and feeding during non-reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non-reproductive periods, respectively, active selection was limited to selection for 4-6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night-time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal-habitat selection was a good predictor of night-time habitat occupancy in a diel-migrating species. Together, these results show that thermal-habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.

Myxozoans as biological tags for stock identification of the Argentine hake, Merluccius hubbsi (Gadiformes: Merlucciidae).

Myxozoans have been successfully used as tags for fish stock identification around the world. However, few studies using myxozoan tags have been carried out in the Southern Atlantic, a region with complex oceanography that constitutes a potentially suitable scenario for testing the utility of myxozoans as indicators. Its usefulness was tested using six samples of Merluccius hubbsi in two different regions of the Argentine Sea. Generalized linear models were performed to assess the effects of fish size and sex, and year and region of capture and selected using the Information Theoretic approach. Three myxozoan species were recorded: Kudoa rosenbuschi, Myxoproteus meridionalis and Fabespora sp. Results of modelling species individually showed differential capabilities for detecting geographical population structure at different spatial scales, with K. rosenbuschi and Fabespora sp. allowing the discrimination of northern and southern stocks, but Fabespora sp. also as a promissory indicator of intrapopulation sub-structure due to different migratory routes during non-reproductive periods. This work confirms that myxozoans offer a set of suitable markers at different spatial scales, which can be selected individually or in any combination, depending on the geographical extent of the study, constituting tools adaptable to the objectives of further research on fish population structure.

Sex- and size-related differences in shell use by the intertidal hermit crab Clibanarius erythropus (Latreille, 1818) (Decapoda: Diogenidae) in the Gulf of Cádiz, southwestern Spain

Clibanarius erythropus (Latreille, 1818) is the dominant hermit crab in intertidal rocky habitats of the Gulf of Cadiz (southwestern Spain). Three different populations of this species were sampled during the reproductive (July 2014) and non-reproductive (October 2014) periods to assess shell use patterns in the field by different demographic groups in absence of interspecific competition for shell-resource use. Irrespective of sampling sites and periods considered, sex ratios were female-biased (2.3 on average), and mean sizes of males were greater than those for females. At least shells from 31 different gastropods were used by C. erythropus in the Gulf of Cadiz. Shell selection was largely determined by the sizes of the hermit crab and shells. As result, a generalist pattern of shell use was displayed by this species. Most hermit crabs with shield length > 4.5 mm were males and the less abundant larger shells were occupied by these large males. Statistically significant sex-related (males vs. females) and size-related (small males vs. large males) differences in shell use were observed at two sampling sites with higher shell diversity, suggesting partial intraspecific partitioning of shell resource. There was a negative effect of carrying relatively heavy/large shells on the stage condition (males and females) and on clutch size of ovigerous females, suggesting that protection from predators was prioritised.