Presence of two mitochondrial genomes in the mytilid Perumytilus purpuratus: Phylogenetic evidence for doubly uniparental inheritance

This study presents evidence, using sequences of ribosomal 16S and COI mtDNA, for the presence of two mitochondrial genomes in Perumytilus purpuratus. This may be considered evidence of doubly uniparental mtDNA inheritance. The presence of the two types of mitochondrial genomes differentiates females from males. The F genome was found in the somatic and gonadal tissues of females and in the somatic tissues of males; the M genome was found in the gonads and mantle of males only. For the mitochondrial 16S region, ten haplotypes were found for the F genome (nucleotide diversity 0.004), and 7 haplotypes for the M genome (nucleotide diversity 0.001), with a distance Dxy of 0.125 and divergence Kxy of 60.33%. For the COI gene 17 haplotypes were found for the F genome (nucleotide diversity 0.009), and 10 haplotypes for the M genome (nucleotide diversity 0.010), with a genetic distance Dxy of 0.184 and divergence Kxy of 99.97%. Our results report the presence of two well-differentiated, sex-specific types of mitochondrial genome (one present in the male gonad, the other in the female gonad), implying the presence of DUI in P. purpuratus. These results indicate that care must be taken in phylogenetic comparisons using mtDNA sequences of P. purpuratus without considering the sex of the individuals.     

A mitochondrial phylogeography of Brachidontes variabilis (Bivalvia: Mytilidae) reveals three cryptic species

This study examined genetic variation across the range of Brachidontes variabilis to produce a molecular phylogeography. Neighbour joining (NJ), minimum evolution (ME) and maximum parsimony (MP) trees based on partial mitochondrial DNA sequences of 16S-rDNA and cytochrome oxidase (COI) genes revealed three monophyletic clades: (1) Brachidontes pharaonis s.l. from the Mediterranean Sea and the Red Sea; (2) B. variabilis from the Indian Ocean; (3) B. variabilis from the western Pacific Ocean. Although the three clades have never been differentiated by malacologists employing conventional morphological keys, they should be ascribed to the taxonomic rank of species. The nucleotide divergences between Brachidontes lineages (between 10.3% and 23.2%) were substantially higher than the divergence between congeneric Mytilus species (2.3–6.7%) and corresponded to interspecific divergences found in other bivalvia, indicating that they should be considered three different species. Analysis of the 16S-rDNA sequences revealed heteroplasmy, indicating dual uniparental inheritance (DUI) of mtDNA in the species of Brachidontes collected in the Indian Ocean, but not in the species in the Pacific nor in the species in the Red Sea and the Mediterranean Sea. When we employed the conventional estimate of the rate of mitochondrial sequence divergence (2% per million years), the divergence times for the three monophyletic lineages were 6–11 Myr for the Indian Ocean and Pacific Ocean Brachidontes sp. and 6.5–9 Myr for the Red Sea and Indian Ocean Brachidontes sp . Thus, these species diverged from one another during the Miocene (23.8–5.3 Myr). We infer that a common ancestor of the three Brachidontes species probably had an Indo-Pacific distribution and that vicariance events, linked to Pleistocene glaciations first and then to the opening of the Red Sea, produced three monophyletic lineages.     

4种生态因子对虎斑乌贼幼体生长与存活的影响

旨在研究温度、盐度、饵料种类、投饵量对虎斑乌贼（Sepia pharaonis）幼体生长与存活率的影响,以确定其生长发育的最佳生态条件,为人工育苗提供理论依据。在室内控制条件下,采用单因子试验研究了不同温度（18、21、24、27、30和33℃）、不同盐度（18、21、24、27、30和33）、不同饵料种类（虾糜、活糠虾、卤虫无节幼体、桡足类、死糠虾、虾糜＋强化卤虫后无节幼体、强化卤虫后无节幼体）、活糠虾不同投饵量（0、2、4、6、8和10 g/d）对虎斑乌贼幼体生长发育的影响。结果显示：不同温度对虎斑乌贼幼体生长影响显著（P〈0.05）,最适温度为24-27℃,在最适温度下,存活率为84.4%-91.1%,特定生长率为4.82%-6.13%,存活率（y）与温度（x）的函数关系为y=-0.15x3＋30.637x-447.002（r2=0.923）。幼体适宜盐度为24-33,最适盐度为27,在最适盐度条件下,其存活率为（90.0±5.29）%,特定生长率为（3.71±0.34）%。投喂7种开口饵料,以活糠虾效果最佳,存活率为（96.7±2.94）%,特定生长率为（3.77±0.23）%;强化卤虫后无节幼体效果次之,存活率为（95.6±2.31）%,特定生长率为（2.54±0.15）%,其余各组培养效果均不理想。投喂活糠虾,随着投饵量的增加,其存活率随之提高,摄食量（y）与个体重（x）的回归方程为y=0.227x-0.063（r2=0.921）。     

Pheromone trail decay rates on different substrates in the Pharaoh's ant, Monomorium pharaonis

Abstract. Many ants use pheromone trails to organize collective foraging. This study investigated the rate at which a well‐established Pharaoh's ant, Monomorium pharaonis (L.), trail breaks down on two substrates (polycarbonate plastic, newspaper). Workers were allowed to feed on sucrose solution from a feeder 30 cm from the nest. Between the nest and the feeder, the trail had a Y‐shaped bifurcation. Initially, while recruiting to and exploiting the feeder, workers could only deposit pheromone on the branch leading to the feeder. Once the trail was established (by approximately 60 ants per min for 20 min), the ants were not allowed to reinforce the trail and were given a choice between the marked and unmarked branches. The numbers of ants choosing each branch were counted for 30 min. Initially, most went to the side on which pheromone had been deposited (80% and 70% on the plastic and paper substrates, respectively). However, this decayed to 50% within 25 min for plastic and 8 min for paper. From these data, the half‐life times of the pheromone are estimated as approximately 9 min and 3 min on plastic and paper, respectively. The results show that, for M. pharaonis, trail decay is rapid and is affected strongly by trail substrate.     

饥饿和再投喂对虎斑乌贼幼体存活、生长和消化酶活力的影响

本文探究了饥饿胁迫与饥饿后再投喂对虎斑乌贼幼体存活率、生长、行为、肝体比、摄食率以及消化酶活力的影响.在室内控制条件下开展了幼体(初始体质量为4.95±0.48 g)的饥饿(0、1、2、3、4、5、6 d)和再投喂(15 d)试验.结果表明: 不同饥饿时间对虎斑乌贼的幼体存活率、体质量降低率、肝体比和消化酶活力影响显著.随着饥饿胁迫时间的增加,其存活率、肝体比呈下降趋势,其中饥饿3 d后,存活率开始明显下降,体质量降低率明显增大,幼体出现喷墨、互相残杀等异常行为;4种消化酶活力呈先下降后上升的趋势,淀粉酶活力以饥饿4 d组最低 (0.07±0.02 U·mg^-1·prot^-1);脂肪酶活力以饥饿2 d组最低(18.47±2.07 U·g^-1·prot^-1),饥饿6 d组最高(57.60±3.98 U·g^-1·prot^-1),胃蛋白酶活力和胰蛋白酶活力以饥饿5 d组(1.98±0.59 U·mg^-1·prot^-1)和饥饿4 d(186.68±20.72 U·mg^-1·prot^-1) 最低.饥饿处理结束后,经15 d再投喂,各试验组存活率、特定生长率、肝体比和摄食率差异显著,幼体的存活率、特定生长率、肝体比和摄食率均与饥饿处理时间呈负相关;饥饿1和2 d组与对照组的存活率、特定生长率和肝肝体比无显著差异,而饥饿3～6 d组显著低于对照组;饥饿1～2 d组的摄食率明显高于对照组,而饥饿6 d组的摄食率明显小于对照组;各组淀粉酶与脂肪酶活力无显著差异,胃蛋白酶与胰蛋白酶活力差异显著,均以对照组最高(胃蛋白酶活力7.06±0.64 U·mg^-1·prot^-1,胰蛋白酶活力914.67±26.54 U·mg^-1·prot^-1),饥饿6 d组最低(胃蛋白酶活力3.21±0.57 U·mg^-1·prot^-1,胰蛋白酶活力660.04±37.92 U·mg^-1·prot^-1).说明虎斑乌贼的幼体饥饿不可逆点(PNR)为第6天,且不能补偿生长.     

Electron probe analysis of strontium in mussel (Bivalvia,Mytilidae) shells: Feasibility of estimating water temperature

Electron microprobe step-scan analyses across the inner nacreous layer of a sectionedMytilus edulis shell revealed no long-term periodic (e.g., seasonal) variation in the concentration of strontium. Similarly, no significant difference was found between a specimen sampled in February (water temperature = 1.3 °C) and one sampled in August (water temperature = 18.0 °C) with regard to the concentration of strontium within the most recently deposited aragonite. Correlation of the amount of strontium within various nacreous regions of the shells of living or fossil mytilids with water temperatures (present or past) is probably not possible through the use of an electron probe, at least to the extent that strontium variation within the nacre ofMytilus edulis is representative of that in nacreous layers of all mytilids.     

Electrophoretic investigation of systematic relationships in the marine mussels Modiolus modiolus L., Mytilus edulis L., and Mytilus galloprovincialis Lmk. (Mytilidae; Mollusca)

Genetic variation was assayed electrophoretically at 13–16 loci in Modiolus modiolus, Mytilus edulis, and Mytilus galloprovincialis. High genetic distance ( D ) values were observed between Modiolus modiolus and Mytilus edulis (1.516 ± 0.523) and between Modiolus modiolus and Mytilus galloprovincialis (1.564 ± 0.539), whereas the distance between Mytilus edulis and M. galloprovincialis (0.167 ± 0.118) was rather low. The systematic status ot Mytilus edulis and M. galloprovincialis is discussed in relation to these lindings and the genetic distance values are used to estimate divergence times which in turn are compared with paleontological estimates. The observations of high average heterozygosity in Modiolus modiolus, and high correlations of locus heterozygosity between taxa are discussed briefly.     

Functional phenotypic plasticity of the endolithic mytilid Leiosolenus curtus (Lischke, 1874) (Bivalvia: Mytilidae)

In Sagami Bay, Japan, Leiosolenus curtus (Lischke, 1874) bores into dead shells of rock barnacles (Tetraclita japonica) in Manazuru, calcareous sand-rock in Oiso, weathered tuff in Miura and agglomerates formed by the tubes of clam worms (Spirobranchus kraussii) in Kanaya. In order to understand the relationships between morphology and environment, the shell morphologies and genetic characteristics of L. curtus, together with the calcium content of the different bored substrata, were analysed. Individuals from Kanaya and Manazuru were characterised by a chalk-like encrustation and a more rounded and inflated shell shape, while those from Oiso and Miura had a striated encrustation. The molecular phylogenetic tree and haplotype network showed that the genetic sequences of the individuals from all investigated localities were very similar, and implied that they belong to the same species. The striated encrustation of the individuals from Oiso and Miura presumably enables them to scrape those residues not dissolved by the mucus secreted by the mantle gland, and thereby to bore into non-calcareous substrata. The more rounded and inflated shell shape of the individuals from Manazuru is thought to be advantageous for boring into thin substrata.     

Relative risk of invasive ants (Hymenoptera: Formicidae) establishing in New Zealand

Abstract

Human‐assisted spread of species poses a major challenge to border security agencies. Ideally, limited resources need to be targeted at species posing the most risk. Climate matching is an important component of assessing risk but often little or no biological information is available to enable detailed modelling. To assess if distribution records alone provide useful establishment predictions we compare the climate in New Zealand and its outlying islands to that found in the current native and introduced ranges of 12 tramp ant species, three of which are already established in New Zealand, using the climate module of BIOSECURE, a risk assessment tool. Eleven species showed a similar general pattern, with mean annual temperature being the climatic variable with the least overlap between the estimated realised niche and the predicted New Zealand niche. The twelfth species, of temperate origin, is less restricted by temperature, but much of New Zealand may have too high a rainfall. The present and future threats posed by tramp ants are discussed in relation to climate limitations.