Asymmetric hybridization between two species of sunfishes (Lepomis: Centrarchidae)

Many of the sunfishes (Centrarchidae) hybridize in natural systems, yet little is known about the interactions among hybridizing individuals in nature. We used allozyme electrophoresis to identify interspecific hybrids between bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) in Lake Opinicon, Ontario, and restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) to identify the maternal parentage of those individuals. All 44 individuals collected and identified electrophoreti-cally as F₁ hybrids had a pumpkinseed mtDNA haplotype, indicating that hybridization between these species in Lake Opinicon is asymmetrical; F₁ hybrids result only from matings between female pumpkinseed and male bluegill.     

A relative growth index of hybridization in sunfishes (genus Lepomis, Centrarchidae)

Sunfish specimens (genus Lepomis) collected from Pinehurst Lake, Ontario, Canada, were identified as bluegill (L. macrochirus), pumpkinseed (L. gibbosus) and their hybrids. Hybridization was studied on the basis of the constants of cross-sectional allometry as, to the best of our knowledge, no attempt has ever been made to study hybridization quantitatively from the relative growth aspect. Two sets of data---one on the pair Y¹/X (head length/standard length) and the other on the pair Y²/X (body depth/standard length)--- were analysed, with the following objectives: (i)A statistical method of analysing hybrid index based on cross-sectional allometry was first presented and then Y¹/X-data analysed by this method, and (ii)data Y²/X were analysed to show that in some particular situations analysis for hybridization by methods other than the hybrid index appraoch may be more appropriate. Results of the analyses were discussed.     

Investigating phylogenetic relationships of sunfishes and black basses (Actinopterygii: Centrarchidae) using DNA sequences from mitochondrial and nuclear genes

The 32 species of the Centrarchidae are ecologically important components of the diverse fish communities that characterize North American freshwater ecosystems. In spite of a rich history of systematic investigations of centrarchid fishes there is extensive conflict among previous hypotheses that may be due to restricted taxon or character sampling. We present the first phylogenetic analysis of the Centrarchidae that combines DNA sequence data from both the mitochondrial and nuclear genomes and includes all described species. Gene sequence data were collected from a complete mtDNA protein coding gene (NADH subunit 2), a nuclear DNA intron (S7 ribosomal protein intron 1), and a portion of a nuclear DNA protein-coding region (Tmo-4C4). Phylogenetic trees generated from analysis of the three-gene dataset were used to test alternative hypotheses of centrarchid relationships that were gathered from the literature. Four major centrarchid lineages are present in trees generated in maximum parsimony (MP) and Bayesian maximum likelihood analyses (BML). These lineages are Acantharchus pomotis, Micropterus, Lepomis, and a clade containing Ambloplites, Archoplites, Centrarchus, Enneacanthus, and Pomoxis. Phylogenetic trees resulting from MP and BML analyses are highly consistent but differ with regard to the placement of A. pomotis. Significant phylogenetic incongruence between mtDNA and nuclear genes appears to result from different placement of Micropterus treculi, and is not characteristic of relationships in all other parts of the centrarchid phylogeny. Slightly more than half of the 27 previously proposed hypotheses of centrarchid relationships were rejected based on the Shomodaira-Hasegawa test.     

Genetic diversity of dispersed seeds is highly variable among leks of the long-wattled umbrellabird

Frugivorous animals frequently generate clumped distributions of seeds away from source trees, but genetic consequences of this phenomenon remain poorly resolved. Seed dispersal of the palm Oenocarpus bataua by long-wattled umbrellabirds Cephalopterus penduliger generates high seed densities in leks (i.e., multi-male display sites), providing a suitable venue to investigate how dispersal by this frugivore may influence seed source diversity and genetic structure at local and landscape levels. We found moderate levels of maternal seed source diversity in primary seed rain across five leks in northwest Ecuador (unweighted mean alpha diversity α = 9.52, weighted mean α_r = 3.52), with considerable variation among leks (α_r range: 1.81–24.55). Qualitatively similar findings were obtained for allelic diversity and heterozygosity. Higher densities of O. bataua adults around leks were associated with higher values of α_r and heterozygosity (non-significant trends) and allelic diversity (significant correlation). Seed source overlap between different leks was not common but did occur at low frequency, providing evidence for long-distance seed dispersal by umbrellabirds into leks. Our findings are consistent with the idea that seed pool diversity within leks may be shaped by the interaction between density of local trees, which can vary considerably between leks, and umbrellabird foraging ecology, particularly a lack of territorial defense of fruiting trees. Taken as a whole, this work adds to our growing appreciation of the ways resource distribution and associated frugivore foraging behaviors mechanistically shape seed dispersal outcomes and the distribution of plant genotypes across the landscape.     

Gene-gene concordance and the phylogenetic relationships among rare and widespread pygmy sunfishes (genus Elassoma)

Pygmy sunfishes (Elassoma) are primarily lowland species with an interesting biogeographic dichotomy: three species have broad geographic distributions, and three are narrowly distributed (and have been recommended for threatened or endangered status). To test phylogenetic predictions derived from the geographic distributions of pygmy sunfishes and possible historical factors contributing to the threatened/endangered status of the rare species, we reconstructed trees for two mitochondrial genes and introns of three nuclear genes. The pattern and rate of nuclear and mitochondrial sequence evolution were heterogeneous within Elassoma, but relationships were generally concordant across gene trees. Elassoma is monophyletic and, as predicted by geographic distributions, E. evergladei, E. okefenokee, and E. zonatum consistently branch from deeper nodes. Phylogeographic structure in mitochondrial and nuclear genes also supports an early origin of E. zonatum. Phylogenetic analyses of the five loci support widely divergent positions for the rare species E. alabamae. Two rare species, E. boehlkei and E. okatie, are sister taxa and are related to a widespread species, E. evergladei.     

Cold acclimation during the wintering of diapausing pupae of Pieris brassicae (lepidoptera)

• 1.l. A 2 month treatment at 5°C, beginning 14 days after larvonymphal ecdysis, leads to considerable physiological modifications of diapausing Pirn's brassicae pupae.
• 2.2. It leads to mechanisms of cold acclimation which are reflected by increased metabolic rates when measured at different temperatures.
• 3.3. This phenomenon affects energy metabolism as well as protein synthesis, but with different modalities.

     

Drought acclimation among tropical forest shrubs (Psychotria,Rubiaceae)

Summary Mechanisms of dry-season drought resistance were evaluated for five evergreen shrubs (Psychotria, Rubiaceae) which occur syntopically in tropical moist forest in central Panama. Rooting depths, leaf conductance, tissue osmotic potentials and elasticity, and the timing of leaf production were evaluated. From wet to dry season, tissue osmotic potentials declined and moduli of elasticity increased in four and five species, respectively. Irrigation only affected osmotic adjustment by P. furcata. The other seasonal changes in leaf tissue properties represented ontogenetic change. Nevertheless, they made an important contribution to dry-season turgor maintenance. Small between-year differences in dry season rainfall had large effects on plant water status. In 1986, 51 mm of rain fell between 1 January and 31 March, and pre-dawn turgor potentials averaged <0.1 MPa for all five Psychotria species in March (Wright 1991). In 1989, 111 mm of rain fell in the same period, pre-dawn turgor potentials averaged from 0.75 to 1.0 MPa for three of the species in April, and only P. chagrensis lost turgor. The relation between leaf production and drought differed among species. P. limonensis was buffered against drought by the lowest dry-season conductances and the deepest roots (averaging 244% deeper than its congeners) and was the only species to produce large numbers of leaves in the dry season. P. chagrensis was most susceptible to drought, and leaf production ceased as turgor loss developed. For the other species, water stress during severe dry seasons may select against dry-season leaf production.     

Limited hybridisation and introgression despite stocking among endemic Interior Highlands black basses (Centrarchidae: Micropterus)

Aim

Smallmouth Bass (Micropterus dolomieu; SMB) are globally popular among anglers and have been widely introduced (i.e. stocked) for population management and sportfishing. Importantly, stocking was prevalent before cryptic diversity within the SMB complex was known, which now includes three newly elevated species: Neosho Bass (M. velox; NB), Little River Bass (M. sp. cf. dolomieu Little River; LRB) and Ouachita Bass (M. sp. cf. dolomieu Ouachita River; OB). We sought to quantify population structure and hybridisation and introgression in these three recently described species.

Location

Species-level diversity, particularly in the basin-restricted LRB and OB in the Ouachita Mountains within the Central Interior Highlands (CIH), North America, suggests the presence of distinct genetic variation that could be eroded by introgression.

Methods

We estimated interspecific introgression and intraspecific population differentiation in the Smallmouth Bass species complex (SMB-C) using 472 specimens comprising SMB, NB, LRB and OB, including the naturally sympatric Spotted Bass (M. punctulatus; SPB). Genomic samples were genotyped on a SNP panel of 192 loci designed to detect allele-sharing on multiple hierarchical levels.

Results

We found low range-wide hybridisation between species in the SMB-C and SPB (mostly SMB-C backcrosses), and interspecific heterozygosity varied, indicating differential introgression. Range-wide hybridisation between species in the CIH and SMB was similar overall (but mostly F₂ and CIH backcrosses) and was observed in streams with known SMB stocking in connected reservoirs. Interspecific heterozygosity in SMB hybrids was also generally lower, indicating later-generation backcrosses. We found strong population structure in the Ouachita Mountains (LRB and OB).

Main Conclusions

Despite isolated incidences of natural (SPB) and human-mediated (SMB) introgression, genomic identity appears intact in endemic LRB and OB, suggesting potential ecological or behavioural isolating mechanisms preventing cross-species reproduction. Our findings reveal that genetic variation remains in cryptic, basin-restricted species in the Ouachita Mountains ecoregion that may be managed for long-term conservation.     

Cold acclimation and oxygen consumption in the thymus

Mitochondrial uncoupling protein 1 is usually associated with brown adipose tissue but has recently been discovered in rat and mouse thymus. We wished to establish whether there was a thermogenic role for UCP 1 in thymus and thus examined the effect of 5 weeks cold-acclimation on rat thymus tissue abundance, thymocyte oxygen consumption, thymus mitochondrial abundance, uncoupling protein 1 expression and function. We found that thymocytes from cold-acclimated rats had oxygen consumption rates 8 times less than those from rats held at room temperature and that thymocytes from cold-acclimated rats or rats kept at room temperature were noradrenaline insensitive. In addition, we found that thymus tissue or mitochondrial abundance was not increased after cold-acclimation. However uncoupling protein 1 expression per unit mass of mitochondria was increased after cold-acclimation, as determined by immunoblotting (∼ 1.7-fold) and GDP binding (∼ 1.5-fold). Consistent with our protein expression data, we also observed an increased, state 4 (∼ 1.5-fold), GDP-inhibitable (∼ 1.3-fold) and palmitate activatable (∼ 1.6-fold) oxygen consumption rates in isolated thymus mitochondria. However, extrapolation of our data showed that cold-acclimation only increased the amount of UCP 1 per gram of thymus tissue ∼ 1.2-fold. Taken together, we conclude that UCP 1 does not have a thermogenic role in thymus.     

Mitochondrial genomes and phylogeny of the ocean sunfishes (Tetraodontiformes: Molidae)

We determined the complete nucleotide sequences of the mitochondrial genomes for the three currently recognized species of ocean sunfish: Mola mola, Masturus lanceolatus, and Ranzania laevis (Tetraodontiformes: Molidae). Each genome contained the 37 genes as found in teleosts, with the typical gene order in teleosts. Bayesian, maximum-likelihood, and maximum-parsimony analyses were conducted with the data set comprising concatenated nucleotide sequences from 36 genes (excluding the ND6 gene) of three molids and four outgroups (three tetraodontiforms plus a caproid). The resultant trees supported monophyly of the Molidae and its intrarelationships ((Mola, Masturus), Ranzania), which were congruent with previous morphology-based hypotheses.     

Cold acclimation and oxygen consumption in the thymus

Mitochondrial uncoupling protein 1 is usually associated with brown adipose tissue but has recently been discovered in rat and mouse thymus. We wished to establish whether there was a thermogenic role for UCP 1 in thymus and thus examined the effect of 5 weeks cold-acclimation on rat thymus tissue abundance, thymocyte oxygen consumption, thymus mitochondrial abundance, uncoupling protein 1 expression and function. We found that thymocytes from cold-acclimated rats had oxygen consumption rates 8 times less than those from rats held at room temperature and that thymocytes from cold-acclimated rats or rats kept at room temperature were noradrenaline insensitive. In addition, we found that thymus tissue or mitochondrial abundance was not increased after cold-acclimation. However uncoupling protein 1 expression per unit mass of mitochondria was increased after cold-acclimation, as determined by immunoblotting (approximately 1.7-fold) and GDP binding (approximately 1.5-fold). Consistent with our protein expression data, we also observed an increased, state 4 (approximately 1.5-fold), GDP-inhibitable (approximately 1.3-fold) and palmitate activatable (approximately 1.6-fold) oxygen consumption rates in isolated thymus mitochondria. However, extrapolation of our data showed that cold-acclimation only increased the amount of UCP 1 per gram of thymus tissue approximately 1.2-fold. Taken together, we conclude that UCP 1 does not have a thermogenic role in thymus.     

Gene-flow between populations of cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) is highly variable between years

Both large and small scale migrations of Helicoverpa armigera Hübner in Australia were investigated using AMOVA analysis and genetic assignment tests. Five microsatellite loci were screened across 3142 individuals from 16 localities in eight major cotton and grain growing regions within Australia, over a 38-month period (November 1999 to January 2003). From November 1999 to March 2001 relatively low levels of migration were characterized between growing regions. Substantially higher than average gene-flow rates and limited differentiation between cropping regions characterized the period from April 2001 to March 2002. A reduced migration rate in the year from April 2002 to March 2003 resulted in significant genetic structuring between cropping regions. This differentiation was established within two or three generations. Genetic drift alone is unlikely to drive genetic differentiation over such a small number of generations, unless it is accompanied by extreme bottlenecks and/or selection. Helicoverpa armigera in Australia demonstrated isolation by distance, so immigration into cropping regions is more likely to come from nearby regions than from afar. This effect was most pronounced in years with limited migration. However, there is evidence of long distance dispersal events in periods of high migration (April 2001-March 2002). The implications of highly variable migration patterns for resistance management are considered.     

Tempo of hybrid inviability in centrarchid fishes (Teleostei: Centrarchidae)

Hybrid viability decreases with divergence time, a pattern consistent with a so-called speciation clock. However, the actual rate at which this clock ticks is poorly known. Most speciation-clock studies have used genetic divergence as a proxy for time, adopting a molecular clock and often far-distant calibration points to convert genetic distances into age. Because molecular clock assumptions are violated for most genetic datasets and distant calibrations are of questionable utility, the actual rate at which reproductive isolation evolves may be substantially different than current estimates suggest. We provide a robust measure of the tempo at which hybrid viability declines with divergence time in a clade of freshwater fishes (Centrarchidae). This incompatibility clock is distinct from a speciation clock because speciation events in centrarchids appear to be driven largely by prezygotic isolation. Our analyses used divergence times estimated with penalized likelihood applied to a phylogeny derived from seven gene regions and calibrated with six centrarchid fossils. We found that hybrid embryo viability declined at mean rate of 3.13% per million years, slower than in most other taxa investigated to date. Despite measurement error in both molecular estimated ages and hatching success of hybrid crosses, divergence time explained between 73% and 90% of the variation in hybrid viability among nodes. This high correlation is consistent with the gradual accumulation of many genetic incompatibilities of small effect. Hybrid viability declined with the square of time, consistent with an increasing rate of accumulation of incompatibilities between divergent genomes (the snowball effect). However, the quadratic slope is due to a lag phase resulting from heterosis among young species pairs, a phenomenon rarely considered in predictions of hybrid fitness. Finally, we found that reciprocal crosses often show asymmetrical hybrid viabilities. We discuss several alternative explanations for this result including possible deleterious cytonuclear interactions. Speciation-clock studies have been a small cottage industry recently, but there are still novel insights to be gained from analyses of more taxonomic groups. However, between-group comparisons require more careful molecular-clock calibration than has been the norm.     

Lysozyme resistance in Streptococcus suis is highly variable and multifactorial

Background

Streptococcus suis is an important infectious agent for pigs and occasionally for humans. The host innate immune system plays a key role in preventing and eliminating S. suis infections. One important constituent of the innate immune system is the protein lysozyme, which is present in a variety of body fluids and immune cells. Lysozyme acts as a peptidoglycan degrading enzyme causing bacterial lysis. Several pathogens have developed mechanisms to evade lysozyme-mediated killing. In the present study we compared the lysozyme sensitivity of various S. suis isolates and investigated the molecular basis of lysozyme resistance for this pathogen.

Results

The lysozyme minimal inhibitory concentrations of a wide panel of S. suis isolates varied between 0.3 to 10 mg/ml. By inactivating the oatA gene in a serotype 2 and a serotype 9 strain, we showed that OatA-mediated peptidoglycan modification partly contributes to lysozyme resistance. Furthermore, inactivation of the murMN operon provided evidence that additional peptidoglycan crosslinking is not involved in lysozyme resistance in S. suis. Besides a targeted approach, we also used an unbiased approach for identifying factors involved in lysozyme resistance. Based on whole genome comparisons of a lysozyme sensitive strain and selected lysozyme resistant derivatives, we detected several single nucleotide polymorphisms (SNPs) that were correlated with the lysozyme resistance trait. Two SNPs caused defects in protein expression of an autolysin and a capsule sugar transferase. Analysis of specific isogenic mutants, confirmed the involvement of autolysin activity and capsule structures in lysozyme resistance of S. suis.

Conclusions

This study shows that lysozyme resistance levels are highly variable among S. suis isolates and serotypes. Furthermore, the results show that lysozyme resistance in S. suis can involve different mechanisms including OatA-mediated peptidolycan modification, autolysin activity and capsule production.     

The effect of Peruvian small-scale fisheries on sunfishes (Molidae)

Reports were compiled of sunfish (family Molidae) by-catch in Peruvian small-scale fisheries and sunfish by-catch rates were estimated using data from shore-based and onboard monitoring programmes. A total of 114 sunfishes were reported in the longline and gillnet fisheries along the Peru coast from 2005 to 2017. Systematic monitoring effort of small-scale gillnets leads to an estimate of between 23 and 352 individuals captured annually by the fleet fishing from the northern port of Salaverry and central ports of Ancon and Chorrillos and suggests that the actual number captured by the Peruvian gillnet fleet is in the thousands of individuals. Thus, Peruvian small-scale fisheries have the potential to greatly affect populations of these still poorly studied species. Moreover, new occurrence locations are reported for the newly described Mola tecta, which was only observed south of 11° S. Because of physical similarities among Mola species it was difficult to identify sunfishes to the species level and thus further studies (e.g., genetics) will be required to provide more detailed information on individual species vulnerability to by-catch in Peruvian waters.     

Cold acclimation of forage grasses in relation to pink snow mould (Microdochium nivale) resistance

The aim of our work is to investigate the changes in phenolic level, PAL activity and heat production rate induced during pre-hardening at 12°C and cold acclimation at 2°C of the forage grasses Festulolium, meadow fescue, tall fescue and Italian ryegrass in relation to their resistance to snow mould caused by Microdochium nivale. Meadow fescue and tall fescue were most resistant to M. nivale infection, while Italian ryegrass demonstrated the least resistance to this fungus inoculation. Festulolium, meadow fescue and tall fescue responded similarly to low temperature, while Italian ryegrass demonstrated considerable disturbance of energy balance and lower phenolic concentration, which could explain a higher susceptibility of the latter species to infection by M. nivale. The enhanced level of phenolic compounds, probably utilised for cell wall lignification as well as equilibrium of the metabolic activity observed in meadow fescue and tall fescue, is very important for both cold and pathogen-resistance mechanisms. The studied Festulolium cultivar ‘Felopa’, a hybrid of the Lolium multiflorum and Festuca pratensis genomes, was characterised by changes in biochemical parameters similar to the resistant meadow fescue and tall fescue.     

Analysis of a meristic trait for hybridization in sunfishes (genus Lepomis)

Necessity of a thorought study of hybridization, following the breakdown of reproductive isolating mechanisms between naturally occurring populations, has been felt by biologists in geneeral and ichthyologists in particular. In this connection a formula for ‘hybrid index’ developed mainly by Hubbs & Kuronuma (1942) and Hubbs, Hubbs & Johnson (1943) has widely been in use, to test the assumption of hybridity and to study the mode of inheritance. Misra, Bateson & Keenleyside (1970) gave statistical methods of analysing hybrid indices estimated for characters of the ‘continuous’ type, and also provided a numerical example. Recently Misra (1971) gave a method of doing similar analysis for hybrid indices estimated for meristic characters, but no example was provided, as data were not available to him. This paper presents a study of hybridization in the sunfishes (genus Lepomis) of Pinehurst Lake, Ontario, Canada, based on the number of scales below the lateral line; the primary purpose of the study is to show the complete computational procedure involved in the application of the method of Misra (1971), so that those users of the method who are mainly interested in the applied aspects of the method, can bypass the mathematics easily.