Maladaptive sex ratio adjustment by a sex-changing shrimp in selective-fishing environments.

1. Selective harvesting is acknowledged as a serious concern in efforts to conserve wild animal populations. In fisheries, most studies have focused on gradual and directional changes in the life-history traits of target species. While such changes represent the ultimate response of harvested animals, it is also well known that the life history of target species plastically alters with harvesting. However, research on the adaptive significance of these types of condition-dependent changes has been limited. 2. We explored the adaptive significance of annual changes in the age at sex-change of the protandrous (male-first) hermaphroditic shrimp and examined how selective harvesting affects life-history variation, by conducting field observations across 13 years and a controlled laboratory experiment. In addition, we considered whether plastic responses by the shrimp would be favourable, negligible or negative with respect to the conservation of fishery resources. 3. The age at sex-change and the population structure of the shrimp fluctuated between years during the study period. The results of the field observations and laboratory experiment both indicated that the shrimp could plastically change the timing of sex-change in accordance with the age structure of the population. These findings provide the first concrete evidence of adult sex ratio adjustment by pandalid shrimp, a group that has been treated as a model in the sex allocation theory. 4. The sex ratio adjustment by the shrimp did not always seem to be sufficient, however, as the supplement of females is restricted by their annual somatic growth rate. In addition, adjusted sex ratios are further skewed by the unintentional female-selectivity of fishing activity prior to the breeding season, indicating that the occurrence of males that have postponed sex-change causes sex ratio adjustment to become unfavourable. 5. We conclude that the plastic responses of harvested animals in selective fishing environments must be considered in efforts to conserve wild animal resources, because such responses can become maladaptive.

Correction to: Behavioral assay and chemical characters of female sex pheromones in the hermit crab Pagurus filholi.

[This corrects the article DOI: 10.1007/s10164-017-0507-y.].

Morphological and morphometric variability in the zoea I larvae of Pugettia quadridens (De Haan, 1839): looking for reliable characters for taxonomic studies on the genus Pugettia Dana, 1851 (Majoidea: Epialtidae).

The larval morphology of Pugettia quadridens (De Haan, 1839) has been described several times, but the lack of voucher specimens (both larvae and spent females), makes it impossible to verify whether the remarkable heterogeneity, which has been described by the different authors, are due to intra-specific variability. We re-described the morphological and morphometric features of the first zoeal stage of the species, depositing voucher specimens for future examination by the scientific community. We used four females that were collected in the same locality in Hakodate Bay, Japan, and found significant morphological and morphometric intra-specific variability, both within and among clutches. One important variation was the setal count on the endopod of maxilla (3-4, rarely 5), which have been considered in previous studies to be a key character to distinguish species within genus Pugettia Dana, 1851. The size differences were rather striking, and the mean carapace length of the largest clutch (0.73 ± 0.04 SD mm) was up to 0.1 mm larger than the smallest one (0.63 ± 0.02 mm). We establish herein a solid taxonomic background for further larval descriptions of species of Pugettia with reliable characters and recommend the use of different clutches to prevent insufficient morphological descriptions due to intra-specific variability.

Behavioral assay and chemical characters of female sex pheromones in the hermit crab Pagurus filholi.

Males of the hermit crab Pagurus filholi perform assessment behavior toward females, as a preliminary step of precopulatory guarding, during the reproductive season. It is known that such behavior is elicited by female sex pheromones, but the compounds involved have never been characterized in this species. Several experiments were conducted to develop a reliable bioassay along with purification procedures to identify potential compounds with pheromonal activity in Pagurus filholi. We developed a bioassay protocol to assess pheromonal activity by using an empty shell with cotton containing either artificial seawater (control) or test water. We measured and compared the time duration of male assessment behavior toward each shell if the test water contained female sex pheromones. Ultra-filtering of seawater samples potentially containing pheromones showed that the compound was <1 kDa in molecular weight. Males showed precopulatory assessment behavior toward "female conditioned" water samples treated with open column purification and eluted with MeOH, suggesting that compounds triggering male behavior were low polar molecules. Molecules with pheromonal activity were not volatile after freeze drying, effective even after heating to 90 °C, and remained active in seawater at 12 °C even after 6 days from sample collection, which suggests a rather stable characteristic of the female sex pheromones of this species.