Invertebrate Biology最新文献

In the present study, two new species of velvet worm, Opisthopatus, from the Eastern Cape province of South Africa are described. We used both mitochondrial and nuclear DNA sequence data (cytochrome oxidase subunit I [COI] and 18S rRNA subunit [18S]) to explore the possibility that species boundaries in Opisthopatus have been underestimated. A previous fine-scale phylogeographic study of the velvet worm Opisthopatus amaxhosa demonstrated the presence of two distinct clades, of which the first could be assigned to O. amaxhosa and the second represented a novel as yet undescribed species. In addition, specimens of Opisthopatus from the Valley of Desolation, Camdeboo Nature Reserve, Graaff-Reinet, were not assigned to a new species in the most recent taxonomic revision because of the limited number of specimens. Following recent collection and scanning electron microscopy, we assigned the Graaff-Reinet specimens to Opisthopatus camdebooi sp. nov. and the second lineage in sympatry with O. amaxhosa we described as Opisthopatus baziya sp. nov. The application of four species delimitation methods (Assemble Species by Automatic Partitioning [ASAP], Poisson Tree Processes [PTP], generalized mixed Yule-coalescent model [GMYC], and Species Tree and Classification Estimation, Yarely [STACEY]) generally revealed congruent groupings across clades, suggesting that the alpha taxonomic diversity in Opisthopatus has been underestimated. The continued discovery of new velvet worm species in poorly or unsampled areas suggests that several novel species might still be undescribed in South Africa. Collectively, our results suggest that fine-scale sampling is critical to detect and describe the biodiversity of other saproxylic taxa.

Catecholaminergic neurons are abundant in molluscs and are involved in a variety of behaviors such as feeding, respiration, learning, and locomotion. However, previous identification of these neurons has relied almost exclusively on immunohistochemistry using antibodies, which have not been fully validated for use in molluscs. We employed tissue-specific quantitative PCR in adults of Lymnaea stagnalis (a pulmonate gastropod) and whole-mount in situ hybridization in larvae to both quantify and visualize messenger RNA of the catecholamine synthesis enzyme, tyrosine hydroxylase (TH). TH messenger RNA was found to localize primarily in the foot and the central nervous system, with smaller quantities present in the cephalic sensory organs. Additionally, we performed western blots that validated a popular antibody used as a marker for catecholaminergic neurons in molluscs. Taken together, these data indicate that TH messenger RNA is present in the central and peripheral nervous system of L. stagnalis and support the specificity of past immunohistochemical labeling of the TH protein. These findings have potentially broad implications, given the wide range of biological processes that have been studied in L. stagnalis.

Selection of food particles for consumption by larvae impacts nutritional gain needed for growth, development, and metamorphosis. Past work has suggested that molluscan larvae are capable of collecting food within a narrow size range. Recent studies have found evidence of size-independent food selection in molluscan larvae, but relatively little is known about the characteristics of particles that larvae preferentially capture. Therefore, we conducted experiments with the larvae of two mussels, Mytilus trossulus and Mytilus edulis, to determine whether they are selective feeders, and if so, whether we could determine the characteristics of particles selected as food. We fed larvae microalgae and polystyrene microspheres of different sizes, nutritional content, surface charge, and hydrophobicity. We found that for both species, there was no effect of size on particle selection for particles 2–8 μm, but, surprisingly, these two congeners preferentially captured particles with different characteristics. Larvae of M. trossulus preferentially captured particles that were more hydrophilic and had a more negative surface charge, but there was no effect of nutritional content. The larvae of M. edulis showed a different pattern; they preferentially captured particles with low surface charge and greater food value, but hydrophobicity did not affect selection. Larvae of these two congeners are indeed selective in which particles they collect but appear to be using different rules for selection. More work is needed to determine whether there are any general patterns that govern particle selection for larvae and mechanisms that could produce the observed patterns. Such work is needed to help us to determine whether individual species use different rules or whether there are general patterns in the types of particles larvae select.

The present study aimed to analyze the occurrence and prevalence, infestation rate and intensity, host–guest colonization pattern, morphometric relationships, and spatiotemporal distribution of the African pea crab (Afropinnotheres monodi) inhabiting the shell of Mediterranean mussels (Mytilus galloprovincialis) from the Algarve coast and Ria Formosa lagoon (southern Portugal). Sampling campaigns were performed with a trimestral periodicity in 2018–2019 and comprised 13 collecting sites distributed in the Ria Formosa, along the Algarve coast, and in an offshore mussel farm. Altogether, 10,109 individuals of M. galloprovincialis in a broad range of sizes (9.0–91.2 mm in shell length) were sampled, among which 571 host mussels (14.6–73.6 mm in shell length) contained a total of 598 individuals of A. monodi, corresponding to an infestation rate of 5.6% (prevalence rate of 5.9% due to multiple occurrences). The sample of pea crabs also covered an extensive range of sizes (1.7–14.5 mm in carapace width) and included eight juveniles, 163 males, and 427 females (82 hard females and 345 soft females, of which 128 were non-ovigerous and 217 ovigerous). Overall, hard (13.9%) and soft (58.5%) females prevailed over males (27.6%), corresponding to female-biased sex ratio of 1 male:2.6 females. In terms of infestation intensity, 95.4% of host mussels contained a single pea crab, with multiple infestations (two or three crabs inside a single mussel) being more frequent in the lagoon than along the coast. Morphometric relationships between host shell length and pea crab carapace width were highly correlated (r values ranged .218–.631), although there were no significant differences between sexes or female demographic categories and maturity stages. Overall, the present study provided further insights into the colonization of M. galloprovincialis by A. monodi.

Among polyclad flatworms, many species are known to develop indirectly via long-lived planktotrophic larvae, whereas the rest hatch as adult-like juveniles. Such adult-like hatchlings have been presumed to represent direct development. However, we report evidence that hatchling polyclads of several genera feed in the plankton on large prey. These ciliated swimmers, despite apparently lacking means to concentrate food or even detect it at a distance, subdue and consume fast-moving active-swimming plankters such as crustacean larvae and copepods, or molluscan veligers. We describe feeding events in captivity using videomicroscopy and identify several wild-caught predatory pelagic polyclad larvae to genus or species level by DNA barcoding. Remarkably, one of these types is identified unambiguously with a species previously observed as Müller's larvae, which live as conventional planktotrophs on a diet inferred to consist of small phytoflagellates. Therefore, we conclude first that although so-called direct-developing polyclad flatworms may hatch with juvenile-like morphology, at least some of these are functionally larvae. Second, these soft-bodied ciliated larvae are neither lecithotrophs nor conventional planktotrophs feeding on unicellular algae, but pelagic predators; indeed, this may constitute the first demonstration that pelagic polyclads eat zooplankton. Third, some species of polyclad have at least a triphasic life cycle, in which a first larval stage lives in the plankton and feeds on primary producers, followed by a second larval stage that remains in the plankton to feed by macrophagous carnivory, before presumably settling to the benthos for adult life.

Many species are shifting their ranges and being forced to rapidly respond to novel stressful environmental conditions. Colonizing individuals experience strong selective forces that favor the expression of life history traits notably affecting dispersal and reproductive rates in newly invaded habitats. Limited information is currently available on trait variation within the invasive range despite being critical for understanding ecological and evolutionary factors that drive the process of range expansion of invasive species. Here we evaluated life history shifts in the widely introduced Asian clam Corbicula cf. C. fluminea within its invaded range. Through an exhaustive literature search, we obtained data for 17 invasive populations of this clam from different ecosystems worldwide. We tested the relationship between population and individual parameters relevant to the process of range expansion. Our main results are that recently introduced populations of clams were characterized by (a) low density and low rate of population increase, (b) earlier reproduction in slow-growing populations of clams, and (c) no effect of density on population increase. All populations of the Asian clam analyzed in this study, which are fixed for one genotype (the lineage called Form A/R), experienced different selective environments in the introduced range. These findings support the perspective that adaptive phenotypic plasticity favored the expression of traits that maximize fitness in recently established populations, which faced stronger r-selective forces relative to long-established ones. We discuss the role of plasticity in facilitating rapid adaptation and in increasing the likelihood of populations to overcome difficulties associated with low densities and low population increase in newly invaded areas.

The superficially simple ciliated planktonic larvae of hoplonemerteans have been assumed to be lecithotrophic direct developers, even though many develop from such small eggs that it is hard to imagine how they could give rise to a viable juvenile without some phase of larval feeding. Indeed, attempts to raise such larvae to settlement without food invariably fail. Observations that some hoplonemertean larvae are found in plankton samples at a range of sizes, and much larger than hatchlings, suggest that they must indeed feed somehow. Because these so-called planuliform larvae lack apparent means to concentrate suspended algae or other unicellular food, one alternative hypothesis is that they are planktonic predators that hunt large prey. Here we provide direct evidence that this is indeed the case for six distinct species of hoplonemerteans. We recorded wild-caught larvae of Paranemertes californica, Paranemertes sp., Gurjanovella littoralis, Emplectonema viride, Carcinonemertes epialti, and Ototyphlonemertes sp. attacking, subduing, and devouring pelagic crustaceans, including barnacle nauplii, cyprids, copepods and their nauplii, and others. Although there is no doubt that some hoplonemerteans are genuine lecithotrophs, our evidence suggests that many species in this group both feed and grow during an extended planktonic larval period. This conclusion has important consequences for biogeographic and life history studies in this group, because it implies enhanced potential for long-distance dispersal. More broadly, the possibility that many animal larvae are actually carnivores invites reconsideration of prevailing stereotypes about metazoan developmental modes and the trade-offs between them.

In the article by Castanaro and Lasker (2003), errors were made in scaling of some of the images. The errors were discovered while examining the data for another project. We remeasured the photos and reanalyzed the data. Some results differed slightly from those reported in the original publication. Growth rates were generally higher than reported in the original analyses, and the proportion of branches that suffered negative growth was lower in the reanalysis. The primary result (that clipped colonies had greater rates of branch origination) was unchanged, but in the reanalysis we found that the magnitude of that effect was different between the two study sites. We also report differences between new and old branches in the linear growth rate that depended on the treatment. Branches present at the time of the clipping had higher growth on clipped colonies compared to similar branches on unclipped colonies, probably reflecting the conversion of existing branches to actively growing source branches (also called mother branches).

Caribbean Pseudopterogorgia spp. have been reassigned to the genus Antillogorgia, and references to Pseudopterogorgia have been changed accordingly.

Of the colonies from Abaco, 12 of the 15 that were clipped to four branches and 10 of those clipped to 10 branches were used in the new analyses. All 28 of the original control colonies were used. Four of the images used in the original analysis of the colonies from San Salvador were lost, and consequently the reanalyses are based on nine of the 15 colonies that were clipped to four branches, 14 colonies that were clipped to 10 branches, and 11 unclipped controls. We used the program ImageJ (Schneider et al., 2012) to label and measure photos of colonies, and we used the vegan package (v2.5-6; Oksanen et al., 2019) in R 3.6.3 (R Core Team, 2020) to conduct new permutational analyses of variance (PERMANOVA).

We reanalyzed 2281 branches that were present on colonies at the start of the experiment identified from the 1999 photos of the colonies used in the analyses. Fewer of the branches had negative growth than reported in the original publication. Overall, 64.3% had positive growth and 35.1% had negative growth. More branches on severely clipped colonies (reduced to four branches; 72.4%) underwent positive growth compared to colonies that were clipped to 10 branches (65.3%) or not clipped (62.6%). Similar levels of positive growth occurred at the Abaco (64.7%) and San Salvador (63.5%) sites.

Zoologists have long tried to culture the limnoterrestrial heterotardigrades associated with bryophytes and lichens without success. By carefully observing heterotardigrades in the genera Echiniscus, Pseudechiniscus, and Viridiscus over many months, we determined that these organisms feed on chloroplasts and cytoplasm from the cells of moss (typically moss protonema), and on the single-celled green algae associated with the moss (typically Chlorella vulgaris). We also determined that the cryptogams they associate with, and hence the heterotardigrades themselves, spend more time in a dried state than do most eutardigrades, which are more easily cultured. Taking these observations into account, we varied food, water, and desiccation cycle conditions with the aim of developing a viable culturing protocol for heterotardigrades. We used this experimentally derived protocol to maintain laboratory cultures of the tardigrades Echiniscus sp., Pseudechiniscus aff. P. ramazzotti and Viridiscus viridianus, which regularly produced new eggs and hatchlings. Both moss and algae from their natural habitats were used as food sources, and a small layer of rain or spring water was added every morning and allowed to partially evaporate overnight. Furthermore, the organisms were more likely to lay eggs on a dense mat of moss protonema, grown by inserting tips of moss branches into a solidified KCM–agar medium. The medium also provided a walking substrate for the tardigrades, and possibly a source of cations. Crucially, the cultures were allowed to dry out completely every 10 days for a period of at least 3 days. Moss in the culture dish significantly improved the chances of the tardigrades coming out of their desiccation-resistant states successfully. The ability to culture heterotardigrades makes these organisms available for modern genomics and other studies with implications for understanding desiccation resistance mechanisms beyond those studied in a few model eutardigrade species.

Parasites may influence their hosts in multiple ways, ranging from physiological changes and behavioral modifications, to altering life history traits. One fitness component that is often considered in relation to parasitism is host fecundity. The larval acanthocephalan parasite, Profilicollis altmani, commonly infects the Pacific mole crab, Emerita analoga; yet this parasite's effect on the crab's fecundity is unknown. Consequently, we examined the effects of acanthocephalan parasitism on the fecundity of this mole crab species. Crabs were collected from the swash intertidal zone in Monterey Bay, CA, and the following parameters were quantified: crab body size (carapace length) and weight, egg-bearing status (nongravid and gravid), egg number and diameter, total volume and weight of egg mass, and their developmental stages (from newly laid eggs to recognizable zoea larval stage). Parasite prevalence, intensity of infection, and body size of larval cystacanths (measured as volume) were assessed. Host fecundity was positively correlated with both body size and body weight. No differences in egg weight were found between uninfected and infected crabs. Similarly, no difference in crab body weight at various embryonic developmental phases was documented between uninfected and infected crabs. Cystacanth volumes in infected nongravid and infected gravid crabs were not significantly different. Our study suggests that the parasite P. altmani does not have any appreciable effect on the fecundity of E. analoga and that female mole crabs undergo normal reproduction and maintain robust population sizes in their natural environments. Our findings thus appear to moderate the pervasive notion of a major impact of parasitism on host reproduction.