Congeneric Species Research Articles

Life cycle traits, secondary production and DNA barcode of Oxyurella ciliata Bergamin, 1939 (Crustacea, Branchiopoda, Anomopoda, Chydoridae)

This study the life cycle and quantify the secondary production of the cladoceran Oxyurella ciliata under controlled conditions in a laboratory and use molecular biology as a tool to investigate its genetic characteristics. The organisms were collected from Baia do Gerente, a pond from the Pantanal region, MS state, Brazil. They were acclimatized, maintained at a controlled temperature (25 ± 1 °C) and photoperiod (12/12h light-dark), fed with the microalgae Raphidocelis subcapitata and observed daily to obtain the data. O. ciliata had a high total egg production of 34.18 ± 9.68 eggs/female and an average longevity of 58.50 ± 16.30 days. These values differed from those previously reported for O. longicaudis, another congeneric species. There was an exponential growth of biomass until instar 6 and the largest secondary production was from the young to the adult phase, which corresponds to the beginning of the reproductive phase. The molecular data revealed that the genetic divergence between the sequence of O. ciliata and that of O. longicaudis is approximately 18 %, which seems high considering that both belong to the same genus. Comparing life cycle data and DNA Barcode, Oxyurella ciliata and O. longicaudis are very distant and have distinct morphological and biological characteristics, such as: body size, egg size, growth, fertility, longevity and development times. This study highlights the importance of molecular studies and information on the life cycle of neotropical cladocerans, in an integrated way, to have a better taxonomic and ecological interpretation of the species.

Temperature and immune challenges modulate the transcription of genes of the ubiquitin and apoptosis pathways in two high-latitude Notothenioid fish across the Antarctic Polar Front.

Thermal variations due to global climate change are expected to modify the distributions of marine ectotherms, with potential pathogen translocations. This is of particular concern at high latitudes where cold-adapted stenothermal fish such as the Notothenioids occur. However, little is known about the combined effects of thermal fluctuations and immune challenges on the balance between cell damage and repair processes in these fish. The aim of this study was to determine the effect of thermal variation on specific genes involved in the ubiquitination and apoptosis pathways in two congeneric Notothenioid species, subjected to simulated bacterial and viral infections. Adult fish of Harpagifer bispinis and Harpagifer antarcticus were collected from Punta Arenas (Chile) and King George Island (Antarctica), respectively, and distributed as follows: injected with PBS (control), LPS (2.5mg/kg) or Poly I:C (2mg/kg) and then submitted to 2, 5 and 8°C. After 1week, samples of gills, liver and spleen were taken to evaluate the expression by real-time PCR of specific genes involved in ubiquitination (E3-ligase enzyme) and apoptosis (BAX and SMAC/DIABLO). Gene expression was tissue-dependent and increased with increasing temperature in the gills and liver while showing an opposite pattern in the spleen. Studying a pair of sister species that occur across the Antarctic Polar Front can help us understand the particular pressures of intertidal lifestyles and the effect of temperature in combination with biological stressors on cell damage and repair capacity in a changing environment.

A new species of Thrixopelma (Araneae: Theraphosidae: Theraphosinae) from southern Peru

ABSTRACT This work aims to describe a new species of Thrixopelma Schmidt, 1994 from southcentral Peru in the Department of Cusco. Thrixopelma choquequirao sp. nov. can be easily distinguished from congeneric species by the low number of labial cuspules, a very long palpal tibia, morphology of the male palpal bulb and female spermathecae. Currently the genus Thrixopelma comprises seven formally described species which inhabit Perú and Ecuador, distributed in Amazonian rainforest, Coastal Dry Forest, and Andean Dry Forest.

Characterisation of the mitochondrial genome and phylogenetic analysis of Toxocara apodemi (Nematoda: Ascarididae).

We first sequenced and characterised the complete mitochondrial genome of Toxocara apodeme, then studied the evolutionary relationship of the species within Toxocaridae. The complete mitochondrial genome was amplified using PCR with 14 specific primers. The mitogenome length was 14303 bp in size, including 12 PCGs (encoding 3,423 amino acids), 22 tRNAs, 2 rRNAs, and 2 NCRs, with 68.38% A+T contents. The mt genomes of T. apodemi had relatively compact structures with 11 intergenic spacers and 5 overlaps. Comparative analyses of the nucleotide sequences of complete mt genomes showed that T. apodemi had higher identities with T. canis than other congeners. A sliding window analysis of 12 PCGs among 5 Toxocara species indicated that nad4 had the highest sequence divergence, and cox1 was the least variable gene. Relative synonymous codon usage showed that UUG, ACU, CCU, CGU, and UCU most frequently occurred in the complete genomes of T. apodemi. The Ka/Ks ratio showed that all Toxocara mt genes were subject to purification selection. The largest genetic distance between T. apodemi and the other 4 congeneric species was found in nad2, and the smallest was found in cox2. Phylogenetic analyses based on the concatenated amino acid sequences of 12 PCGs demonstrated that T. apodemi formed a distinct branch and was always a sister taxon to other congeneric species. The present study determined the complete mt genome sequences of T. apodemi, which provide novel genetic markers for further studies of the taxonomy, population genetics, and systematics of the Toxocaridae nematodes.

Intersection of coral molecular responses to a localized mortality event and ex situ deoxygenation.

In July 2016, East Bank of Flower Garden Banks (FGB) National Marine Sanctuary experienced a localized mortality event (LME) of multiple invertebrate species that ultimately led to reductions in coral cover. Abiotic data taken directly after the event suggested that acute deoxygenation contributed to the mortality. Despite the large impact of this event on the coral community, there was no direct evidence that this LME was driven by acute deoxygenation, and thus we explored whether gene expression responses of corals to the LME would indicate what abiotic factors may have contributed to the LME. Gene expression of affected and unaffected corals sampled during the mortality event revealed evidence of the physiological consequences of the LME on coral hosts and their algal symbionts from two congeneric species (Orbicella franksi and Orbicella faveolata). Affected colonies of both species differentially regulated genes involved in mitochondrial regulation and oxidative stress. To further test the hypothesis that deoxygenation led to the LME, we measured coral host and algal symbiont gene expression in response to ex situ experimental deoxygenation (control = 6.9 ± 0.08 mg L-1, anoxic = 0.083 ± 0.017 mg L-1) in healthy O. faveolata colonies from the FGB. However, this deoxygenation experiment revealed divergent gene expression patterns compared to the corals sampled during the LME and was more similar to a generalized coral environmental stress response. It is therefore likely that while the LME was connected to low oxygen, it was a series of interconnected stressors that elicited the unique gene expression responses observed here. These insitu and ex situ data highlight how field responses to stressors are unique from those in controlled laboratory conditions, and that the complexities of deoxygenation events in the field likely arise from interactions between multiple environmental factors simultaneously.

First report of Macrochaetus sericus Thorpe, 1893 and Lecane tenuiseta Harring, 1914 (Rotifera: Monogononta) from Jammu waters (J&K), India

Water bodies, apart from having aesthetic value, harbor a great diversity of both macro and microorganisms. Rotifers or wheel animalcules are cosmopolitan aquatic invertebrates that play a key role in aquatic food chain. Presently, two species of rotifers (Macrochaetus sericus & Lecane tenuiseta) have been recorded for the first time from Jammu. M. sericus is first record from Union territory of J&K while L. tenuiseta has already been reported from Kashmir. During the one year study period, M. sericus was observed in the plankton sample during the monsoon season while L. tenuiseta was collected from the periphytic zone during the winter season. M. sericus differed from related congeneric species by absence of anal segment and anal spines. L. tenuiseta is distinguished by its long separated claws and long toes. The first report of these two species from Jammu has further expanded their distributional ranges in the Indian subcontinent.

Genetic and Distribution Data of the Bramble Shark Echinorhinus brucus (Bonnaterre, 1788) and the Prickly Shark Echinorhinus cookei Pietschmann, 1928 to Better Reconstruct Their Conservation Status.

Elasmobranch species show low resilience in relation to anthropogenic stressors such as fishing efforts, loss of habitats, and climate change. In this sense, the elasmobranch populations appear to be at risk of extinction in many cases. Despite conservation researchers making efforts to implement knowledge, the information on the biology, reproduction, distribution, or genetic structure of some species is still scattered, often caused by the occurrence of species in inaccessible habitats. Echinorhinus brucus is a deep benthic shark evaluated as "Endangered" on which little information is available, particularly about its geographical range and genetic structure, while E. cookei is listed as "Data Deficient". Echinorhinus brucus belongs to the Echinorhinidae family, and its unique congeneric species is E. cookei. The main morphological diagnostic characteristic of both species is the presence of denticles with different shapes and patterns on the derma. In the present paper, mitochondrial COI and NADH2 sequences were retrieved from both E. brucus and E. cookei species, and analyses were conducted by applying different models of phylogenetic inference. Sequences of E. brucus captured in the Indian Ocean (IOS) did not cluster with the Atlantic E. brucus counterparts (AOS) but instead with E. cookei sequences; the different models showed an overlapping tree topology. Concurrently, a review of the historical and recent captures of the two species was carried out. The worldwide distribution of E. brucus excludes the Pacific Ocean area, where E. cookei occurs, and is characterised by presumably current local extinctions in the North Sea and the western Mediterranean Sea. The dataset describes two definite areas of significantly high abundance of E. brucus located in the Atlantic Ocean (Brazil) and the Indian Ocean (India). These areas suggest zones for conservation plans, especially considering the two lineages identified through molecular approaches.

Race to the poles: the thermal response of the transcriptome of two range-expanding pelagic amphipod species

IntroductionHyperiid amphipods of the genus Themisto are a key polar zooplankton group in terms of biomass and play an important role as prey for higher trophic levels. They are prone to undergo changes in abundance and distribution in the course of the ongoing environmental changes. In the Southern Ocean, Themisto gaudichaudii is predicted to expand its distribution poleward. In the Arctic, the boreal-Atlantic T. abyssorum increases in abundance, resulting in an increased competition with a genuine polar congener. It is not known, however, whether T. gaudichaudii and T. abyssorum have the potential to efficiently adapt to changing water temperatures at their current distribution range or whether they will be shifting their ranges poleward.MethodsWe exposed the two Themisto species from different geographic populations to temperature-change experiments, a cold treatment and a heat-shock treatment. After that, we carried out transcriptome sequencing to compare gene expression patterns in the different treatments and species.ResultsWe show that under similar heat conditions, T. gaudichaudii differentially expressed more genes (26-fold change) than T. abyssorum. Furthermore, we observed qualitative differences between genetic clusters in T. gaudichaudii.DiscussionThe differences observed between genetic clusters in T. gaudichaudii suggest that evolutionary divergence can be linked to changes in the regulatory pathways involved in temperature stress. These could influence the capacity of each genetic cluster to cope differently with temperature changes. In contrast to its congeneric species, T. abyssorum showed a pronounced adaptive flexibility to thermal stress; it appears to have the ability to continue its poleward expansion but may also cope with increasing temperatures in its current environments. Our findings contribute to understand the response of two range-shifting Themisto species to thermal stress in view of the environmental gradients they encounter throughout their current or future distribution ranges.

Dynamic intraguild interactions between two sympatric and congeneric coccinellid species associated with aphids could explain their coexistence in citrus agroecosystems

Scymnus interruptus and Scymnus subvillosus (Coleoptera: Coccinellidae) are the most frequent aphid predators in Western Mediterranean citrus agroecosystems. Intraguild predation (IGP) between them would be expected, but how IGP might affect their coexistence and biological control function remains unknown. In this work, we assess the frequency of predator encounters in the field and investigate intraguild predation between these two predators in laboratory settings. Different field prey scenarios derived from the field observations were simulated with the two dominant aphid species in this agroecosystem, Aphis gossypii and Aphis spiraecola.Scymnus subvillosus and S. interruptus engaged in IGP but the magnitude and symmetry varied with the prey species and abundance. At high aphid densities, IGP was symmetric and weak, whereas, at low aphid densities, IGP was strong and very asymmetric, with S. interruptus taking the role of the intraguild predator. The developmental time of S. subvillosus was reduced when competing with S. interruptus at high extraguild prey densities. The adult size of both predators under weak IGP also increased even when the developmental time had been reduced.We predict that high aphid infestations in the spring would benefit S. subvillosus, while the strong and asymmetric IGP at low aphid infestations would hinder its coexistence with S. interruptus. Our results give a theoretical explanation to what is observed in the field: S. subvillosus is typically dominant during the high aphid infestations of the spring, whereas S. interruptus increases in relative dominance during the summer and fall when aphid abundance is much less.

Bashimyzon cheni, a new genus and species of sucker loach (Teleostei, Gastromyzontidae) from South China

Bashimyzon, new genus, is here established for Erromyzon damingshanensis, and a new species of the genus is described from the You-Jiang of the Pearl River (=Zhu-Jiang in mandarin Chinese) basin in Guangxi Province, South China. This new genus has a small gill opening above the pectoral-fin base and short pectoral fins extending backwards short of pelvic-fin insertions, both characters combined to separate it from all currently-recognized gastromyzontid genera except Erromyzon and Protomyzon, but differs from the two genera in having a larger gap between the posterior edge of eye and the vertical through the pectoral-fin insertion and very small fleshy lobes posterior to the maxillary-barbel bases. It is further distinct from its most similar genus Erromyzon in having a relatively larger gill opening, fewer branched pectoral-fin rays folded against body, and more posteriorly placed pectoral fins with a shorter fin base. Bashimyzon cheni, new species, and B. damingshanensis, the single congeneric species, differ in number of lateral-line pored scales, body coloration, and cephalic contour, and also in substantial genetic divergence.

Anticancer agents and genetic identification of Pterospermum, an indigenous plant of Sarawak, Malaysia

In Malaysia, Pterospermum is distributed in the states of Peninsular Malaysia, Sarawak, and Sabah. For centuries, the Bidayuh tribe in Sarawak has been using an indigenous plant to cure patients diagnosed with breast cancer. The plant is called Bayur by the tribe, which is the similar local name known for several Pterospermum species in Sarawak, Sabah, and Indonesia. This study was carried out to genetically identify the indigenous plant using the core barcode loci, rbcL and matK, as well as profiling anticancer agents from this plant. Phylogenetic analyses based on both rbcL and matK loci did not show clear species resolution for the indigenous plant, however, the analyses showed consistent relationships among congeneric species of Pterospermum. Interestingly, UHPLC-QQQ/MS analysis showed the presence of anti-cancer agents in the bark extract, thus supporting the potential of the indigenous plant for breast cancer treatment.

The Sympatric Coexistence Mechanism: A Case Study of Two Penahia Species in the Beibu Gulf, South China Sea.

The study of trophic relationships among closely related species plays an important role in deepening our understanding of the resource utilization characteristics, differentiation patterns, and population dynamics of co-occurring species in the same habitat. This research uses two congeneric fish species, Pennahia pawak and Pennahia anea, as examples. Based on a stomach content analysis and a carbon-nitrogen stable isotope analysis, a comparative analysis of their feeding habits and trophic niches is conducted. Additionally, a spatial niche analysis is employed to explore the coexistence and competitive mechanisms between these two closely related fish species. The results show that specialized feeding habits mitigate intraspecific competition as the population densities increase. The carbon and nitrogen stable isotope analysis reveals variations in the feeding habits and trophic levels with body length, indicating adaptive shifts in prey selection. Despite similar food resources, niche differentiation arises due to differences in dominant prey, facilitating coexistence. Differences in spatial niche further contribute to niche separation and coexistence. In resource-limited environments, species such as Pennahia utilize trophic and spatial niche differentiation to collectively exploit resources and achieve coexistence, with implications for fishery management favoring Pennahia resource occupancy capabilities.

Low similarity between parasite communities of ten sympatric carangid species

Host phylogeny and ecological convergence are two factors thought to influence the structure of parasite communities. The aims of this study were to determine the diversity of metazoan parasites of 10 sympatric fish species of the family Carangidae from the southeastern Gulf of California, and to analyze their similarity at infracommunity and component community levels, in order to determine if the host species, particularly those congeneric with similar ecological characteristics, exhibit similar assemblages of parasites. In total, 874 fish specimens were examined and 40 parasite species were identified. The component community was composed by 21 parasite species in Caranx caninus, 20 in C. caballus, 11 in C. vinctus, five in Chloroscombrus orqueta, four in Carangoides otrynter, seven in Hemicaranx leucurus, eight in Selene brevoortii, 14 in S. peruviana, and 11 in Trachinotus rhodopus. The metazoan parasite communities of C. vinctus, Ch. orqueta, H. leucurus, and S. brevoortii are reported here for the first time. The parasite communities of the remaining six carangid species have been reported from regions other than the Gulf of California. All fish species differed significantly regarding the diversity of their parasite infracommunities. This possibly is due to different patterns of habitat use among fish species, and because of the differential host specificity among parasite taxa. Nonetheless, when the analysis was restricted to common parasite species, some fish showed similar parasite infracommunities, particularly congeners of the genus Selene as well as C. caballus and C. vinctus. The component communities of species of Selene were highly similar (>65%), but the three species of Caranx were not. This result supports the hypothesis that congeneric fish species with similar ecological filters harbor similar parasite communities. However, the difference observed between C. caninus and C. caballus suggests that these species, despite being evolutionary and ecologically related, have different physiological or immunological characteristics (compatibility filters) that may result in different parasite communities.

New species of Bolbapium Boucomont, 1910 (Coleoptera: Geotrupidae) from Brazil

Bolbapium Boucomont, 1910 is a Neotropical genus of Geotrupidae with 22 known species. In this paper, we describe Bolbapium vazdemelloi sp. nov. in Southwestern Bahia, Brazil. This new species is distinguished from congeneric species by its unique combination of morphological characters: cephalic tubercle adjacent to each eye; pronotum with little expanded bidentate tubercle; parameres symmetric, with acute and divergent apex. The new species was incorporated into a previously published identification key for Bolbapium.

Drought, temperature, and moisture availability: understanding the drivers of isotopic decoupling in native pine species of the Nepalese Himalaya.

The Himalayas experienced long-term climate changes and recent extreme weather events that affected plant growth and the physiology of tree species at high-elevation sites. This study presents the first statistically robust δ18OTR chronologies for two native pine species, Pinus roxburghii, and Pinus wallichiana, in the lower Nepalese Himalaya. The isotope chronologies exhibited 0.88‰ differences in overall mean isotope values attributed to varying elevations (460-2000m asl). Comparative analysis of climate response using data sets from different sources and resolutions revealed the superiority of the APHRODITE (Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation) data set calibrated for the South Asian Summer Monsoon (SASM)-dominated region. Both species exhibited negative correlations with monsoon precipitation and positive correlations with temperature. However, during the peak monsoon season (July-August), daily resolved climate data disentangled statistically insignificant relationships, and revealed that δ18OTR is influenced by atmospheric moisture. Both congeneric species showed a decoupling between the chronologies after 1995. However, no significant change in air moisture origin and monsoon regime between the study sites was observed, indicating a consistent dominant moisture source during different monsoon seasons. Besides, we also observed the decreased inter-series correlation of both δ18OTR chronologies after 1995, with P. wallichiana experiencing a steeper decrease than P. roxburghii. The weakening correlations between and within the chronologies coincided with a regional drought during 1993-1995 in both sites, highlighting the strong regulation of local climate on the impact of regional extreme climate events. Our findings emphasise the importance of employing climate data with optimal spatial and temporal resolution for improved δ18OTR-climate relationships at the intra-annual scale while considering the influence of site-specific local environmental conditions. Assessing climate data sets with station data is vital for accurately interpreting climate change's impact on forest response and long-term climate reconstructions.

Geographic variation in incubation temperatures promoting viable offspring production in broadly co-distributed turtles.

Organisms whose early life stages are environmentally sensitive produce offspring within a relatively narrow range of suitable abiotic conditions. In reptiles, development rate and survival are often maximized if incubation temperatures remain under 31°C, though this upper bound may vary within and among species. We addressed this expectation by comparing responses to egg incubation at 30°C versus33°C in congeneric turtle species pairs with broad syntopic geographic distributions. In the two softshell turtles (Apalone spp.), the greatest changes in development rate and phenotypic variance were observed in the northernmost population, which had a low survival rate (40%) at 33°C. The presumably suboptimal temperature (33°C) for northern populations otherwise yielded 76%-93% survival rates and fast swimming speeds in more southern populations. Still, in one species, northern hatchlings incubated at 33°C matched the elevated speeds of their southern counterparts, revealing a countergradient response. In northern populations of the two map turtles (Graptemys spp.), survival was also reduced (28%-60%) at 33°C and the development rate (relative to 30°C) increased by up to 75%. Our experiments on divergent taxa with similar nesting ecologies substantiate that the optimal thermal range for offspring production is variable. These findings encourage further work on how population- and species-level differences relate to local adaptation in widely distributed oviparous species.

Climate-driven mitochondrial selection in lacertid lizards.

The mitochondrion, which is an intracellular organelle responsible for most of the energy-producing pathways, can have its genome targeted for climate-driven selection. However, climate-driven mitochondrial selection remains a sparsely studied area in reptiles. Here, we reported the complete mitochondrial genome sequence of a lacertid lizard (Takydromus intermedius) and used mitogenomes from 54 species of lacertid lizards to study their phylogenetic relationships and to identify the mitochondrial genes under positive selection by climate. The length of the complete mitochondrial genome sequence of T. intermedius was 17,713 bp, which was within the range of lengths (17,224-18,943) ever reported for Takydromus species. The arrangement of mitochondrial genes in T. intermedius was the same as in other congeneric species. The 54 lacertid species could be divided into three geographically and climatically different clades. We identified three mitochondrial genes (ATP6, ATP8, and ND3) under positive selection by climate, and found that isothermality, temperature seasonality, precipitation of wettest month, and precipitation seasonality were the most important climatic variables contributing to the gene selection.

Hormonal response to recurrent seasonal stress in coastal and mountain scabiouses growing in their natural habitat: linking ABA and jasmonates with photoprotection.

Plant species distribution across ecosystems is influenced by multiple environmental factors, and recurrent seasonal stress events can act as natural selection agents for specific plant traits and limit species distribution. For that, studies aiming at understanding how environmental constraints affect adaptive mechanisms of taxonomically closely related species are of great interest. We chose two Scabiosa species inhabiting contrasting environments: the coastal scabious S. atropurpurea, typically coping with hot-dry summers in a Mediterranean climate, and the mountain scabious S. columbaria facing cold winters in an oceanic climate. A set of functional traits was examined to assess plant performance in these congeneric species from contrasting natural habitats. Both S. atropurpurea and S. columbaria appeared to be perfectly adapted to their environment in terms of adjustments in stomatal closure, CO2 assimilation rate and water use efficiency over the seasons. However, an unexpected dry period during winter followed by the typical Mediterranean hot-dry summer forced S. atropurpurea plants to deploy a set of photoprotective responses during summer. Aside from reductions in leaf water content and Fv/Fm, photoprotective molecules (carotenoids, α-tocopherol and anthocyanins) per unit of chlorophyll increased, mostly as a consequence of a severe chlorophyll loss. The profiling of stress-related hormones (ABA, salicylic acid and jasmonates) revealed associations between ABA and the bioactive jasmonoyl-isoleucine with the underlying photoprotective response to recurrent seasonal stress in S. atropurpurea. We conclude that jasmonates may be used together with ABA as a functional trait that may, at least in part, help understand plant responses to recurrent seasonal stress in the current frame of global climate change.

The first unique‐headed bug (Hemiptera, Enicocephalomorpha) from Cretaceous Iberian amber, and the Gondwanan connections of its palaeoentomological fauna

AbstractEnicocephalomorpha, also known as unique‐headed bugs, are a seldom‐collected infraorder of heteropteran insects whose evolutionary relationships have puzzled entomologists for more than a century. Unique‐headed bugs are exceptionally rare in the fossil record, which hinders our understanding of the morphological transformations of the lineage across time and also affects the calibration of molecular clock estimates used to date the origins of the infraorder. Here, we report the discovery of Enicocephalinus ibericus sp. nov. from Iberian amber in the Ariño deposit in Spain, early Albian (Early Cretaceous) in age. The new species represents the second oldest fossil enicocephalomorphan to date, and the second record of this infraorder from European deposits. Remarkably, the closest relative of E. ibericus is the congeneric E. acragrimaldii Azar from Lebanese amber that is c. 20 myr older (Barremian), indicating a long‐term persistence of the Enicocephalinus lineage across geological time. A review of the existing literature enabled us to record a total of 20 congeneric insect species that have been found in both Lebanese and Iberian ambers, suggesting the existence of previously underappreciated entomofaunal connections between southern Laurasia (the European archipelago) and northern Gondwana during the Cretaceous. We show that the palaeoentomological record holds remarkable potential for elucidating the faunistic exchanges and palaeobiogeographical patterns in the peri‐Tethyan region during the Cretaceous.

Evidence for hybridization-driven heteroplasmy maintained across generations in a ricefish endemic to a Wallacean ancient lake.

Heteroplasmy, the presence of multiple mitochondrial DNA (mtDNA) haplotypes within cells of an individual, is caused by mutation or paternal leakage. However, heteroplasmy is usually resolved to homoplasmy within a few generations because of germ-line bottlenecks; therefore, instances of heteroplasmy are limited in nature. Here, we report heteroplasmy in the ricefish species Oryzias matanensis, endemic to Lake Matano, an ancient lake in Sulawesi Island, in which one individual was known to have many heterozygous sites in the mitochondrial NADH dehydrogenase subunit 2 (ND2) gene. In this study, we cloned the ND2 gene for some additional individuals with heterozygous sites and demonstrated that they are truly heteroplasmic. Phylogenetic analysis revealed that the extra haplotype within the heteroplasmic O. matanensis individuals clustered with haplotypes of O. marmoratus, a congeneric species inhabiting adjacent lakes. This indicated that the heteroplasmy originated from paternal leakage due to interspecific hybridization. The extra haplotype was unique and contained two non-synonymous substitutions. These findings demonstrate that this hybridization-driven heteroplasmy was maintained across generations for a long time to the extent that the extra mitochondria evolved within the new host.