Enhanced condition in dogwhelks, Nucella lapillus (L.) living under mussel hummocks

Dogwhelks, Nucella lapillus eat both barnacles and mussels, Mytilus edulis. However, mussels are dangerous prey because they can snare and immobilize dogwhelks with their byssi. Despite this danger, adult dogwhelks are common inside mussel hummocks or stacks found on mature mussel beds. The whelks live in debris-filled chambers within the hummocks, unsnared by byssi. Evidence is presented to show that this is a highly favourable microhabitat for dogwhelks. Condition index (CI) measurements showed that mean CI for “hummock” dogwhelks was 20.99 in early spring, 29.65 in midsummer and 34.86 in early winter. In comparison, CI values for dogwhelks from nearby barnacle zones were 20.13, 25.03 and 24.66 respectively. The summer and winter CI values of “hummock” dogwhelks were enhanced to a highly significant extent. Data are also presented to show that shore elevation or dogwhelk shell height (over the size range of animals studied) had no confounding effect on this result. Predicted flesh and shell mass values for a standard 25 mm high whelk showed that occupation of hummocks was associated with a thin-walled shell morphology, and that the shell mass became proportionately lower in summer and early winter. A feeding experiment showed that CI rises slowly, even in dogwhelks fed to satiation on mussels. Dogwhelks were taken from the barnacle zone in March 1997 and either fed to satiation on Mytilus or starved, whilst being held in seawater at ambient seawater temperature. The CI of fed dogwhelks rose from 19.7 to 27.4 in 3 months, while that of starved Nucella fell from 19.7 to 16.3. In the meantime, the CI of dogwhelks in situ in the barnacle zone had risen from 19.7 to 23.8. Hence, 3 months' satiation ration had led to a nett 3.6 unit rise in CI; starvation to a nett 7.5 unit fall. All of the changes in CI were due to changes in flesh mass; shell mass was stable. Since “hummock” dogwhelks collected in early winter have a CI value about 10.2 units greater than barnacle zone dogwhelks, this indicates that “hummock” dogwhelks are long-term inhabitants of this microhabitat.     

Winter territoriality and its implications for the breeding ecology of White-throated Dippers Cinclus cinclus

Capsule: Pairs of White-throated Dippers Cinclus cinclus which defended winter territories bred earlier than non-territorial individuals, but there was no difference in reproductive success.

Aims: The effect of winter territoriality on breeding ecology has rarely been studied in resident birds. We carried out a preliminary investigation of whether winter territorial behaviour and territory size affect the timing of reproduction, breeding territory size and reproductive success in a riverine bird, the White-throated Dipper.

Methods: We monitored an individually marked population of White-throated Dippers in the UK. Wintering individuals were classified as either territorial or ‘floaters’ according to their patterns of occurrence and behaviour, and their nesting attempts were closely monitored in the subsequent months. Winter and breeding territory sizes were measured by gently ‘pushing’ birds along the river and recording the point at which they turned back.

Results: All birds defending winter territories did so in pairs, but some individuals changed partners before breeding. Territorial pairs that were together throughout the study laid eggs significantly earlier than pairs containing floaters and those comprising territorial birds that changed partners. However, there were no significant differences in clutch size, nestling mass or the number of chicks fledged. There was no relationship between winter territory length and lay date or any measure of reproductive success, although sample sizes were small. Winter territories were found to be significantly shorter than breeding territories.

Conclusion: Winter territoriality may be advantageous because breeding earlier increases the likelihood that pairs will raise a second brood, but further study is needed. Territories are shorter in winter as altitudinal migrants from upland streams increase population density on rivers, but this may also reflect seasonal changes in nutritional and energetic demands.     

Aspects of the ecology of an exposed shore population of dogwhelks Nucella lapillus (L.)

Summary Up to the third year of life Nucella lapillus (L.) could be aged in the laboratory and in the field using shell characters. Monthly counts along transects on an exposed rocky shore have shown that the age groups behave differently, dogwhelks in their first year migrating upshore, and returning to lower levels in the second year. Adults (three years or older) lived and laid egg capsules in the low shore. The most favourable situation for subsequent hatching of these capsules was where they were permanently submerged in sea water.The first requirement of recently hatched young was probably protection from water movement, but they soon gegan feeding on small mussels. The shell height attained by the end of the first winter was related to winter temperatures, but the main growing season was June to November. Adult size was attained in two years, after which the individuals did not usually grow, but those which did grow during the third or succeeding years may have been nonbreeders or have been castrated by the trematode Parorchis acanthus.The age structure of the population suggested that mortality rate decreased with age, and this was confirmed by calculating annual mortality rates for the first three years of life. Heavy mortality in the low shore during the first winter was due mainly to predation by purple sandpipers. In succeeding winters mortality was low, and predation, the main mortality factor, was restricted to the summer months. At this time Cancer pagurus was the most voracious predator, but it was active mainly in the low shore, and the upshore distribution of second year dogwhelks, which were preferred to other age groups, age groups also led to a more economical use of environmental resources, namely food, winter aggregation sites and breeding sites.     

Sampling strategy related to fish distribution, with particular reference to the Norfolk Broads

Large-scale movements of fish within a complex freshwater system such as the Norfolk Broads can give rise to erroneous sampling data if the extent of these movements is not fully appreciated. The Norfolk Broads habitat is briefly described, and data are presented showing that mean estimates of standing crop in the broads vary from <1gm^-2 in the winter to 9.4 gm^-2 in the summer. The widespread nature of the phenomenon is demonstrated by winter and summer data from five broads, and a more detailed picture of the seasonal changes is shown by an intensive 2-year study on one of these broads. Winter aggregations of fish have been found in sites adjacent to rivers connected with the broads, with densities of up to 36.7 fish m^-2 and a biomass of 1787 gm^-2. Accurate overall estimates of fish standing crop can only be obtained when fish are maximally dispersed during the summer months.     

Mating aggregation of a stink bug,Megacopta punctissimum (Montandon) (Heteroptera: Plataspidae)

Summary Adults of a stink bug,Megacopta punctissimum, form aggregations on stems of the bush-clover,Lespedeza crytobotria, in spring. They do not oviposit there, but feed and mate within aggregations. Oviposition is made on other leguminous plants such as the kudzu-vine,Pueraria lobata. Mean size of aggregations (groups of two or more individuals which sit on a stem at distance less than 3 cm from their nearest neighbors) consisted of 4.4 individuals. The sex ratios within aggregations were similar to overall sex ratio of the population including solitary individuals (0.58). More than 50% of females found in aggregations were copulating. Percentage of femalesin copula in larger aggregations was higher than that in smaller aggregations, and this difference was considered to be caused by the higher chance of sexual enconters in larger aggregations. It was suggested that the aggregation of this species on the bush-clover is not a ‘harem’ (a male monopolizes a group of females reported in some other stink bugs) but is mating aggregation to raise the chance of mating. This work was partially supported by Grant-in-Aid (No. 56480039) from the Ministry of Education, Science and Culture.     

Rana cascadae tadpoles aggregate with siblings: an experimental field study

Previous laboratory studies have shown that Rana cascadae larvae preferentially associated with siblings over non-siblings in choice tests. This study, conducted during three consecutive summers, tests the hypothesis that R. cascadae larvae aggregate nonrandomly with respect to sibship in natural ponds. Pairs of sibships were reared in separate tanks or together in the same tank in the laboratory. Each sibship within a pair was then stained with neutral red or methylene blue dye and released together in a natural pond. Over a period of several days, aggregations of tadpoles within test ponds were repeatedly captured, censused for sibship composition, and released. In control tests, two groups of tadpoles from the same sibship were dyed different colors and released together. In total, 25 different tests were conducted using tadpoles from 31 sibships and 456 aggregations were sampled. The distribution of color compositions of aggregations in control tests did not differ from an expected random distribution. Color compositions of aggregations in experimental tests differed from controls and from an expected random distribution. Aggregations in these tests tended to be dominated by one of the two colors (sibships). We conclude that R. cascadae tadpoles recognize and prefer to aggregate with siblings in natural field conditions. Circumstances of early rearing (i.e., whether tadpoles were reared with siblings or in mixed sibling/non-sibling groups) had no influence on preferences to associate with siblings, but there was an inverse correlation between group size and sibling association.     

The aggregation of polar cod (Boreogadus saida) in the deep Atlantic layer of ice-covered Amundsen Gulf (Beaufort Sea) in winter

During the Circumpolar Flaw Lead System Study (CFL, 2007–2008), large aggregations of polar cod were detected in winter in the Amundsen Gulf (Western Canadian Arctic) using the EK60 echosounder of the CCGS Amundsen research icebreaker. Biomass estimated over 10 months reached a maximum of 0.732 kg m⁻² in February. Aggregations were encountered only in the presence of an ice cover from December to April. The vertical extent of the aggregations was dictated by temperature and zooplankton prey distribution. In winter, polar cod generally occupied the relatively warm deep Atlantic Layer (>0°C), but a fraction of the densest aggregations occasionally followed zooplankton prey up into the cold Pacific Halocline (−1.6 to 0°C). The diel vertical migration of polar cod was precisely synchronized with the seasonally increasing photoperiod. Throughout winter, polar cod aggregations migrated to progressively deeper regions (from 220 to 550 m bottom depths) in response to increasing light intensity, presumably to avoid predation by visual predators such as the ringed seal. Comparing Amundsen Gulf and Franklin Bay indicates that the entrapment of polar cod in embayments during winter is an important mechanism to provide marine mammal predators with dense concentrations of their main prey within their diving range.     

Energetics of the muricid gastropod Thais (Nucella) lapillus (L.)

Multivariate analysis of the physiological energetics of Thais (Nucella) lapillus (L.) was used to predict combinations of salinity and temperature at which scope for growth and reproduction will be positive. The scope for growth correlated positively with change in energy content at 15 and 20°C. The results suggest that energetic constraints set limits to capacity adaptation at ≈ 22‰ salinity, in agreement with field observations of the species distribution limit within estuaries. The zone of resistance adaptation is limited to salinities 15‰, probably because of an inefficiency in volume regulation at lower salinities. Growth of these dogwhelks is suppressed at minimum winter (5°C) and maximum summer (20°C) temperature, largely due to suppression of feeding. Constraints imposed by physiological energetics are important for an understanding of the ecology of this species, and may explain some features of seasonal change in behaviour, e.g. aggregations for purposes of egg-laying in the winter.     

Family-based winter territoriality in western bluebirds, Sialia mexicana: the structure and dynamics of winter groups

Winter residency is characteristic of the majority of cooperatively breeding birds, but the composition and dynamics of winter groups have been examined in relatively few. In 1996-1998, we examined winter territoriality in the western bluebird, a year-round resident that shows a limited degree of helping behaviour in central coastal California, U.S.A. In spring, most western bluebirds breed as socially monogamous pairs, but a small proportion of pairs (3-16%) have additional breeding-age males helping at the nest, usually assisting parents or brothers. We found that year-round residents commonly wintered in family groups that defended territories similar to those used in spring. Winter groups had an even sex ratio and formed early in the autumn, when hatch-year birds dispersed. More females than males left their natal groups to be replaced by an influx of immigrant hatch-year birds. Winter groups typically consisted of breeders and one or two sons from the prior breeding season along with one or more immigrant females. A second period of dispersal occurred in spring when winter groups broke up and most birds other than the breeding pair left the winter territory. When they bred, yearling males and females often bred with unrelated individuals from their winter groups. Sons were more likely to remain on the study area as yearlings when they wintered with both parents than when they wintered with just one parent. We suggest that young males stay the winter due to benefits of remaining in family groups on mistletoe-based winter territories. Subsequent localized dispersal of sons then leads to opportunistic kin-based interactions later in life. Copyright 2001 The Association for the Study of Animal Behaviour.     

Distribution and spacing of Drosophila mycetophaga flies on bracket fungi used as mating arenas

Abstract.

• 1 To understand the nature of male aggregations in Drosophila mycetophaga, data were collected on male and female distribution and male spacing on bracket fungi used as mating arenas in cool rainforests of south-eastern Australia.
• 2 Both males and females appeared to be aggregated among bracket fungi that were used as mating arenas. Females were associated with large male aggregations. The probability of a fungus being occupied increased with its area. However, a multiple Poisson regression analysis suggested that fungus area did not affect female distribution when male number was controlled.
• 3 The presence of female breeding and feeding resources did not determine where aggregations were formed, because there were aggregations on fungi without resources, and fungi with resources were not used more often than those without them.
• 4 D.mycetophaga males did not select and defend territories within bracket fungi, and did not determine female access to areas. However, males were more evenly spaced than expected on the basis of a random distribution, suggesting that males kept apart from each other.
• 5 The distribution of the different sexes and male spacing pattern supports the interpretation that D.mycetophaga has a lek mating system.

     

Predators,Parasites and Heterospecific Aggregations in Chrysomeline Larvae

Gregariousness is a common feature in aposematic insect prey and offers the additional benefit of enhancing the effectiveness of their toxic defences. Aggregations of the aposematic larvae of two species of leaf beetles, Paropsis atomaria and Paropsisterna variicollis, occur together on the same Eucalyptus trees over spring and summer. Conventionally, the colouration of these larvae is thought to provide aposematic protection against vertebrate predators, but supporting evidence is limited. We determine whether environmental preferences contribute to the heterospecific aggregations, and the potential costs for larvae of living in heterospecific aggregations. We surveyed natural aggregations of the larvae of both species in the field and recorded environmental variables of these aggregations. This revealed that heterospecific aggregations occurred more commonly at higher leaf temperatures, and in less visually conspicuous locations. Paropsis atomaria larvae were twice as likely to be found in heterospecific aggregations than Pa. variicollis. Next, we manipulated larval aggregations in the field to investigate the survival and gregarious behaviour of larvae in heterospecific aggregations. The gregarious behaviour of both species of larvae did not differ between heterospecific and monospecific aggregations. Further, the survival of larvae did not significantly differ between heterospecific and monospecific aggregations. We suggest that the preference for P. atomaria larvae to aggregate with Pa. variicollis at higher leaf temperature results in the observed heterospecific aggregations, with a potential benefit of lowerer parasitoidism rates for P. atomaria.     

Behavioural components of prey-selection by dogwhelks, Nucella lapillus (L.), feeding on barnacles, Semibalanusbalanoides (L.), in the laboratory

Adult dogwhelks, maintained on mussels for 60 days before experimentation to reduce prior effects of ingestive conditioning and handling skills appropriate to barnacles, and thence deemed “inexperienced”, preferred the largest barnacles presented to them. Juvenile and adult dogwhelks, maintained on barnacles and deemed experienced, preferred barnacles of intermediate sizes that were correlated with the sizes of the dogwhelks. “Inexperienced” dogwhelks penetrated barnacles significantly more often by drilling than by prising, whereas experienced dogwhelks did the reverse. A predominant tendency to prise open barnacles was developed by previously “inexperienced” dogwhelks after they had eaten six to eight consecutive prey. Larger dogwhelks prised open greater proportions of larger barnacles than did smaller dogwhelks. Experienced adult dogwhelks prised open all barnacles of ≈2-mm opercular diameter but only 20% of those ≈ 6 mm in diameter. The preferred barnacles, 4–5 mm in opercular diameter, were of a size that the experienced adult dogwhelks could prise open in 50% of attacks.Dogwhelks inspected barnacles by crawling over them for ≈20 min when the prey were subsequently rejected and ≈30 min when subsequently eaten. Penetration time and ingestion time were linear functions of barnacle diameter, total handling time ranging from 4–26 h for barnacles of 2.5–2.7 mm opercular diameter. Experienced dogwhelks handled barnacles faster than “inexperienced” dogwhelks, largely because they used the quicker method of penetration by prising whenever possible. The yield of flesh per unit handling time was an accelerating function of barnacle size and, with experience, could be increased by a factor of ≈1.2 for barnacles of 7 mm opercular diameter to ≈2.0 for barnacles of 2 mm opercular diameter. The preference of experienced dogwhelks for barnacles somewhat smaller than the largest available, may have reflected the greater frequency with which these prey could be penetrated by the quicker method of prising. Minimizing handling time could be important in nature if there is a risk to feeding dogwhelks of being displaced by competitors. In the laboratory, 12% of dogwhelks where thus displaced.Barnacles of ≈5 mm opercular diameter were estimated to be slightly more profitable than mussels of ≈17.5-mm shell length to a dogwhelk experienced with barnacles, but less profitable to a dogwhelk that has recently fed extensively on mussels. Dogwhelks, therefore, might switch between diets predominately of barnacles or of mussels if prey of comparable profitabilities change drastically in their relative abundance on the shore.     

Winter biology of the blacknose dace,Rhinichthys atratulus,in a southern Ontario stream

Synopsis The winter habitat of stream-dwelling blacknose dace Rhinichthys atratulus is identified and described from underwater observations in a southern Ontario stream. In late November as water temperatures declined below 5.0°C, dace moved into crevices beneath rubble with a mean maximum diameter of 15.9 cm. Focal point water depth was significantly greater in winter and mid-depth water velocity was significantly faster than measured in the summer. Dace were not observed in open water again until late March when water temperatures increased to 4.0°C. Winter diet analyses which showed minimal feeding were consistent with the seasonal changes in condition factor and percentage body water suggesting a general depletion of body reserves over winter. This physiological change was more pronounced in juveniles.     

The effect of thermal stress on protein composition in dogwhelks (Nucella lapillus) under normoxic and hyperoxic conditions

In this laboratory study, dogwhelks (Nucella lapillus) were collected from the intertidal zone and exposed to 16 °C (ambient), 26.5 °C and 30 °C under normal and hyperoxic conditions respectively. It was shown that there was no thermally induced mortality at 26.5 °C, but that the mortality rate was 40–50% in 30 °C. This mortality rate was reduced to 10% if extra oxygen was provided, indicating that oxygen supply was setting the limit for whole organism thermal tolerance. Tissue samples were then analysed for protein features using two-dimensional gel electrophoresis, and both up and down regulation of proteins were visualised by silver staining and crosswise comparisons of gels from control vs. treated animals. The results clearly show that the protein profiles from dogwhelks exposed to increased water temperatures differ from those of the control, but that increased oxygen availability alleviates these differences thus increasing the similarity between heat-shocked and control animal protein pattern. This implies a more stable protein metabolism and might explain the increased survival of heat-shocked individuals when extra oxygen is supplied.     

Female Leadership During Migration and the Potential for Sex-Specific Benefits of Mass Spawning in the Brown Surgeonfish (Acanthurus nigrofuscus)

Spawning aggregations in coral-reef fishes have been hypothesized to confer any one of several mutually non-exclusive benefits, largely expected to serve the interests of both sexes simultaneously. Here we provide indication that in the brown surgeonfish, Acanthurus nigrofuscus, spawning aggregations may confer a sex-specific benefit. Following tagged individuals en-route to their daily spawning-aggregation site we found that while migrating groups (≤20 fish) consist of both males and females, females tend to occupy the lead position more often than expected by chance. In addition, we found evidence that female A. nigrofuscus divide their daily egg-stock among several spawning bouts within the aggregations. We propose that female leadership en-route to spawning aggregations, together with the potential benefits of multiple female mating, are consistent with a sex-specific benefit to spawning aggregations.     

High‐density aggregations of rodlet cells in the gonads of Greenland halibut Reinhardtius hippoglossoides,a deep‐water marine flatfish

Large aggregations of rodlet cells in the gonads of male and female Greenland halibut Reinhardtius hippoglossoides are reported for the first time. These rodlet cells were not arranged epithelially but rather were found throughout the connective tissue between oocytes (females) or within lymphatic spaces between testicular lobules (males). The reason for large aggregations of rodlet cells in the gonads and not other tissues of this species is uncertain.     

Genetic mark-recapture analysis of winter faecal pellets allows estimation of population size in Sage Grouse Centrocercus urophasianus

The Sage Grouse Centrocercus urophasianus is a species of conservation concern throughout its range in western North America. Since the 1950s, the high count of males at leks has been used as an index for monitoring populations. However, the relationship between this lek-count index and population size is unclear, and its reliability for assessing population trends has been questioned. We used non-invasive genetic mark-recapture analysis of faecal and feather samples to estimate pre-breeding population size for the Parachute-Piceance-Roan, a small, geographically isolated population of Sage Grouse in western Colorado, during two consecutive winters from 2012 to 2014. We estimated total pre-breeding population size as 335 (95% confidence interval (CI): 287–382) in the first winter and 745 (95% CI: 627–864) in the second, an approximate doubling in abundance between years. Although we also observed a large increase in the spring lek-count index between those years, high male count data poorly represented mark-recapture estimates of male abundance in each year. Our data suggest that lek counts are useful for detecting the direction and magnitude of large changes in Sage Grouse abundance over time but they may not reliably reflect small changes in abundance that may be relevant to small populations of conservation concern.     

Odour stimuli affecting autumn migration of Rhopalosiphum padi (L.) (Hemipter: ornoptera)

R. padi gynoparae settling in the canopy of the winter host, Prunus padus, tended to form aggregations. Differences in the degree of exposure to wind, sun, etc., did not satisfactorily explain the aggregated pattern observed. In laboratory experiments, aphids did not distinguish between leaves taken from nearby aggregations and leaves taken far away from aggregations. The results of laboratory olfactometer tests and field trapping studies indicate that R. padi gynoparae produce an aggregation pheromone. Thus the aggregated settling pattern of gynoparae of R. padi can best be explained as a response to an aggregation pheromone.     

Nasal Discs and the Vital Rates of Lesser Scaup

Nasal discs have been used to identify ducks in studies of survival and reproduction. To date, there has not been a comprehensive assessment of nasal-disc effects on the vital rates of wild ducks. We applied nasal discs to 603 juvenile and 784 adult lesser scaup (Aythya affinis) females from a population breeding in southwest Montana, USA, and released 1,399 juvenile and 71 adult females wearing only metal leg bands between June 2005 and September 2016. Using resighting, recapture, and hunter-recovery data collected from those individuals, we estimated survival and recovery probability with multistate capture-recapture models in Program MARK. We also assessed if recovery distance from our study site and pre-breeding and brood-rearing body condition were diminished for females wearing nasal discs. Model-averaged survival probabilities were 0.231 ± 0.035 (SE) for juveniles and 0.482 ± 0.019 for adults released with nasal discs. Survival was 1.8–3.4 times higher for females released with metal leg bands when compared to those released with nasal discs; survival of these juveniles was 0.433 ± 0.049 and 0.693 ± 0.039 for adults. We did not find evidence for recovery probability or recovery distance varying between females that wore nasal discs and those that did not. During the pre-breeding and brood-rearing seasons, we did not find females wearing nasal discs to be in lower body condition when compared to unmarked females. Our comprehensive assessment of nasal discs on wild lesser scaup suggests that survival probabilities estimated from nasal-marked study populations should be cautiously interpreted as minimum estimates. © 2021 The Wildlife Society.     

Spatial and temporal patterns of movement and migration at spawning aggregations of red hind, <Emphasis Type="Italic">Epinephelus guttatus</Emphasis>, in the U.S. Virgin Islands

This study compared the spatial and temporal patterns of red hind, Epinephelus guttatus, movement and migration from annual spawning aggregations on St Thomas (STT) and St Croix (STX), United States Virgin Islands. Around STT E. guttatus migrated 6–33 km from a functional spawning migration area of 500 km² and around STX E. guttatus migrated 5–18 km from an area of 90 km². Similarities between sites were found in regards to timing of movement, temporal and spatial changes in sex ratios, annual and lunar predictability and were synchronized with environmental cues. E. guttatus spawning aggregations in the Virgin Islands occur between the winter solstice (i.e., after December 20) and about February 20 of any year and show a distinctive peak 20–40 days after the winter solstice. Spawning typically occurred during periods of declining seawater temperature and slacking currents within a temperature range of 26–27.5°C and current speed of 2.5–3.5 cm s⁻¹. Males arrived early to spawning sites and stayed longer than females. These gender-based behavioral patterns are important to E. guttatus reproductive dynamics and must be factored into future studies and the design of fisheries regulations to ensure sustainability of spawning aggregation sites. The predictability of E. guttatus spawning aggregations relative to the winter solstice will be extremely beneficial for defining the temporal and spatial aspects of area closures. The consistency and synchrony of movement and migration will improve both the efficiency of planning research and monitoring programs and directing enforcement activities during critical time periods. Applying this knowledge strategically will maximize the limited resources available for research and enforcement and lead to greater protection of spawning aggregations.