Group size and individual ‘personality’ influence emergence times in hermit crabs

Whereas small Pagurus bernhardus (L.) occur in large numbers in the intertidal areas of rocky shores, large hermit crabs living in whelk shells are most uncommon, although they are easily collected by sublittoral dredging. Experiments were carried out to assess the salinity tolerance, and the ability to regulate body volume in a dilute medium, of both small and large hermit crabs. Large, offshore hermit crabs are significantly less tolerant of 60% sea water (100%=34‰ S) than small, littoral specimens. Small littoral crabs increase in weight by about 15% in the first hour in 60% sea water, but increased urine output prevents swelling thereafter; indeed, there is considerable loss in weight, presumably caused by solute loss. Large, offshore, crabs increase in weight by about 15% in the first hour, thus exhibiting a higher permeability to water than small crabs, and continue to increase in weight, since urine output is not sufficient to cope with the water load. Dissections suggest that insufficient release of urine causes the low urine output in large hermit crabs, rather than inadequate production of primary urine. Calculations indicate that the nephropores of large hermit crabs are too small to allow a sufficiently high urine output to remove a large water load, unless greater pressures are developed inside the excretory systems of large hermit crabs than occur in those of small littoral individuals. In view of the soft, flexible nature of the walls of the excretory system and abdomen of P. bernhardus, it seems unlikely that high pressures could be maintained within the excretory system. It is concluded that the stenohalinity of large, offshore hermit crabs may exclude them from the littoral zone, or may be the result of exclusion by other factors, since there will be no selective advantage for large hermit crabs in maintaining the degree of euryhalinity possessed by the small littoral crabs, if the large crabs are confined to the sublittoral zone.

Phylogenetic inferences on HIV-1 transmission

Correlated phenotypic traits (i.e. syndromes) may manifest as associations between different behavioural types or between behavioural and non-behavioural phenotypes. While syndromes research is extensive, correlations involving behavioural type and sensory morphology have yet to be investigated. Sensation is essential in decision-making and should be correlated with behavioural phenotypes involved in risk response, including boldness. We investigated correlations between boldness and sensory capacity in Pagurus bernhardus hermit crabs, taking repeat measures of startle response durations to assess hermit crab personality and predictability. The correlation between startle response and the sensillar density (i.e. number of sensilla per unit surface area) of both chelipeds was assessed using Bayesian-fitted double hierarchical general linear models. Negative correlations between these traits support the existence of a syndrome linking sensory capacity and behavioural type, hereafter distinguished as a 'sensory investment syndrome'. Increasing sensillar density on the major claw also corresponded with reduced within-individual variation, or predictability, in startle response duration. By revealing a correlation between sensory and behavioural phenotypes, our results demonstrate the importance of considering sensory morphology and performance in behavioural ecology and show how sensory investment syndromes might support behavioural strategies that help maximize fitness.

Hitching a ride on a hermit crabs home: Movement of gastropod shells inhabited by hermit crabs

Hermit crab biocoenoses: a worldwide review of the diversity and natural history of hermit crab associates

Less choosy or different preference? Impact of hypoxia on hermit crab shell assessment and selection

Vacancy chains occur when individuals occupy discrete re‐useable resource units, which once abandoned by the current owner can then be occupied by a new owner. In order to enter the newly vacated resource the new owner must first vacate its current resource unit, such that a vacancy chain consists of a series of linked moves between resource units of different value, equivalent to different ‘strata’ in the chain. Vacancy chains may represent an important route by which resources are distributed through populations. Indeed, the arrival of a new resource has the potential to initiate a series of moves propagating beyond the individual that encounters the new resource unit. Thus, the chain participants as a whole may experience ‘aggregate benefits’ from the arrival of the new resource unit. The extent of these benefits, however, may not necessarily be evenly distributed between all chain participants; some individuals could receive greater than average benefits by moving through more than one stratum (‘skipping’) and some individuals could experience a reduction in resource value by moving to a resource unit of lower quality than that occupied initially (a ‘backward move’). Such moves represent deviations from the ‘ideal’ vacancy chains assumed by theory. Here we analyse the aggregate benefits and benefits to individuals participating in vacancy chains of empty gastropod shells in the hermit crab Pagurus bernhardus. We also investigate the effect of predation risk on these two levels of benefits and on chain structure. Adding a new shell at the top of the chain causes an overall increase in shell quality after 24 h but the distribution of benefits between strata in the chain varies with the presence and absence of the predator cue. Although there was significant concordance between chain structure in the presence and absence of the predator cue, the structure was significantly different from an ideal vacancy chain in the absence but not the presence of the predator cue.

Cyclic organochlorines in the hermit crabs Pagurus bernhardus and P. pubescens from the North Sea. A comparison between winter and early summer situation

Littoral hermit crabs, Pagurus bernhardus, show a strong preference for Littorina obtusata shells rather than those of Gibbula species. The fitness consequences, in terms of fecundity, for this shell preference is examined for female crabs. Females in the preferred species produced eggs earlier in the season, produced more eggs in the first brood, and produced a second brood more often than did females in the less preferred species. The smaller brood for Gibbula spp. was not a consequence of egg loss from the pleopods due to an unfavourable shape of shell, but rather reflected lower egg production. It is not clear, however, if this differential reproduction is due to direct costs of carrying an unfavourable shell, i.e. the shell impedes reproduction, or whether crabs compete aggressively for favoured shells so that only crabs of low quality inhabit lowquality shells.

Concentrations of organochlorine compounds in the hermit crab Pagurus bernhardus from the German bight, December 1988 –May 1989

Monoamines and decision making during contests in the hermit crab Pagurus bernhardus

The development of shell preferences by the hermit crab Pagurus bernhardus

A Field Study of Intraspecific Competition for Food in Hermit Crabs (Pagurus bernhardus)

Microplastics are ubiquitous in global marine systems and may have negative impacts on a vast range of species. Recently, microplastics were shown to impair shell selection assessments in hermit crabs, an essential behaviour for their survival. Hermit crabs also engage in ‘rapping’ contests over shells, based on cognitive assessments of shell quality and opponent fighting ability and, hence, are a useful model species for examining the effects of microplastics on fitness-relevant behaviour in marine systems. Here, we investigated how a 5-day microplastic exposure (25 microplastics/litre) affected the dynamics and outcome of 120 staged hermit crab contests. Using a 2 × 2 factorial design, we examined how microplastics (i.e. presence or absence) and contestant role (i.e. attacker or defender) affected various behavioural variables. Significantly higher raps per bout were needed to evict microplastic-treated defenders when attackers were pre-exposed to control conditions (i.e. no plastic). Also, significantly longer durations of rapping bouts were needed to evict control-treated defenders when attackers were pre-exposed to microplastics. We suggest that microplastics impaired defenders' ability to identify resource holding potential and also affected attackers’ rapping strength and intensity during contests. These impacts on animal contests indicate that microplastics have broader deleterious effects on marine biota than currently recognized.

The effect of noise on predator vigilance in Pagurus bernhardus was explored in this study. Latency of the first response, emergence time, and response type were measured from hermit crabs during continuous and variable vessel noise and two controls. The mean (±SE) response latency was longer for the noise treatments (continuous, 18.19 ± 2.78 s; variable, 11.39 ± 1.48 s) than for the controls (ambient, 7.21 ± 0.82 s; silent, 6.66 ± 0.95 s). Response type and emergence time were not significantly affected but were more variable during the noise treatments than during the controls. Noisy conditions may increase predation risk, suggesting potential fitness consequences for invertebrates.