Effects of dams on downstream molluscan predator-prey interactions in the Colorado River estuary.

River systems worldwide have been modified for human use and the downstream ecological consequences are often poorly understood. In the Colorado River estuary, where upstream water diversions have limited freshwater input during the last century, mollusc remains from the last several hundred years suggest widespread ecological change. The once abundant clam Mulinia modesta has undergone population declines of approximately 94% and populations of predators relying on this species as a food source have probably declined, switched to alternative prey species or both. We distinguish between the first two hypotheses using a null model of predation preference to test whether M. modesta was preyed upon selectively by the naticid snail, Neverita reclusiana, along the estuary's past salinity gradient. To evaluate the third hypothesis, we estimate available prey biomass today and in the past, assuming prey were a limiting resource. Data on the frequency of drill holes-identifiable traces of naticid predation on prey shells-showed several species, including M. modesta, were preferred prey. Neverita reclusiana was probably able to switch prey. Available prey biomass also declined, suggesting the N. reclusiana population probably also declined. These results indicate a substantial change to the structure of the benthic food web. Given the global scale of water management, such changes have probably also occurred in many of the world's estuaries.

First elucidation of the life cycle in the family Brachycladiidae (Digenea), parasites of marine mammals.

Digeneans of the family Brachycladiidae are cosmopolitan parasites restricted to marine mammals. Their life cycles are unknown. Phylogenetically, Brachycladiidae are closely related to Acanthocolpidae, parasites of marine teleost fishes. Acanthocolpida typically possess three-host life cycles with gastropods of the superfamily Buccinoidea acting as the first intermediate hosts for most species, and either fishes or bivalves acting as the second intermediate hosts. A few species previously identified as Neophasis differ from other Acanthocolpidae in having naticid gastropods as first intermediate hosts, and both fishes and bivalves as second ones. We assumed that this may indicate an incorrect life cycle description and revised previous data on rediae and cercariae of Neophasis spp. from Cryptonatica affinis (Naticidae) and metacercariae from cardiid bivalves at the White Sea using molecular and morphological approaches. Sequence comparison showed that rediae and cercariae from C. affinis resembling some representatives of the genus Neophasis and metacercariae from bivalves resembling Neophasis oculata belong to the brachycladiid species Orthosplanchnus arcticus. Thus, the life cycle of O. arcticus proceeds as follows: seals serve as the definitive host, C. affinis as the first intermediate host and cardiid bivalves as the second. We found one more type of redia and cercaria in C. affinis which, by molecular evidence, also belongs to Brachycladiidae and is closely related to O. arcticus. Here we refer to them as Brachycladiidae gen. sp. 1 WS. We suggest that Brachycladiidae gen. sp. 1 WS may belong to either Orthosplanchnus or Odhneriella, with beluga whales possibly being the definitive host. Morphological features of O. arcticus and Brachycladiidae gen. sp. 1 WS cercariae are summarised and matched with published data on putatively brachycladiid cercariae. We compare and discuss the diversity of life cycle patterns among Brachycladiidae and Acanthocolpidae, and show that they differ not only in the type of definitive host, but also in both intermediate hosts.

Naticid gastropods from the middle Miocene of western Ukraine.

The paper covers 11 species of naticid gastropods occurring in the lower Serravallian (Upper Badenian) strata of western Ukraine (Central Paratethys). The studied material (over 1,700 naticids) represents six genera and 11 species, of which eight are new: Cochlis odovychenorum, Cochlis ukrainensis, Tectonatica anistratenkorum, Tectonatica pseudoprietoi, Euspira sirenkoi, Payraudeautia ermesi, Payraudeautia sabrinae and Payraudeautia varovtsiana. Additionally, we have also identified Euspira protracta (Eichwald, 1830), Polinices staszici (Friedberg, 1923) and Sinum affinis (Eichwald, 1830). A lectotype of Sinum affinis is designated (ZISP 1/62208). Detailed descriptions of the protoconch and teleoconch morphology of the taxa involved, including SEM images, are presented.

The complete mitochondrial genome of Glossaulax reiniana (Littorinimorpha: Naticidae).

In the present study, the complete mitochondrial genome of Glossaulax reiniana was determined using the next-generation sequencing. The circular genome was found to be 15,254 bp in length and had an overall nucleotide composition of 30.6% A, 14.1% C, 15.8% G, and 39.5% T. Similar to the typical caenogastropod mitochondrial genomes, it contained 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and a potential control origin. All protein-coding genes started with standard initiation codons (ATA and ATG) and ended by TAA or TAG. The lengths of 12S ribosomal RNA and 16S ribosomal RNA were 948 and 1353 bp, respectively. The largest noncoding region considered to contain the origin of replication was 59 bp in length. The complete mitochondrial genome reported here would provide useful information for molecular phylogeny, genetic conservation, and sustainable management of G. reiniana.

Evidence of non-drilling predation by a naticid gastropod in bivalves on Camocim Beach, Ceará, northeastern Brazil

Marine gastropods of the family Naticidaeare worldwide distributed and known for their unusual predatory habits. Due to their wide distribution, the naticids are worldwide studied and known like predators of intertidal bivalves. The present study demonstrates the predation of the naticid gastropod Natica marochiensison the bivalve Donax striatusin the northeastern region of Brazil.

EVIDENCE FROM THE FOSSIL RECORD OF AN ANTIPREDATORY EXAPTATION: CONCHIOLIN LAYERS IN CORBULID BIVALVES.

Conchiolin layers, organic-rich laminae, are characteristic of the shells of corbulid bivalves. The retention of these layers, despite their high metabolic cost, throughout the evolutionary history of Corbulidae has prompted the proposal of several adaptive scenarios to explain the origin and maintenance of these layers. The most widely held hypothesis contends that conchiolin layers are an adaptation for inhibiting drilling by predatory naticid gastropods. However, others suggest that the layers are adaptations to retard shell dissolution in waters undersaturated with calcium carbonate or to increase shell strength in the face of durophagous (shell crushing) predators. In this paper, experiments using recent Corbula (Varicorbula) gibba (Olivi) and observations of corbulids' present natural habitat demonstrate the current utility of conchiolin layers for all three functions: retardation of shell dissolution in waters undersaturated in calcium carbonate, increase of mechanical shell strength, and inhibition of drilling by predatory naticid gastropods. Earlier analyses of the extensive history of naticid predator-corbulid prey interactions suggested that conchiolin layers were an adaptation, a feature that promotes fitness and was built by selection for its current role, for deterring naticid predators. Not only are naticid drillholes widespread in fossil and recent corbulid shells, but an unusually large number of incomplete drillholes terminate unsuccessfully at conchiolin layers. In addition, a phylogenetic analysis of the origin of conchiolin layers and its function to deter naticid predators is consistent with a hypothesis of adaptation for this function. However, this hypothesis is rejected by an examination of fossil Jurassic Corbulomima. These oldest corbulids contained conchiolin layers before the evolution of naticid drilling during the Early Cretaceous. Therefore, conchiolin layers appear to be an exaptation, characters evolved for other usages and later "coopted" for their current role, for defense against drilling predators. The layers may in fact be an adaptation to resist durophagous predation.