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Results for “Reproductive Isolation”

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PubMed2006

At daybreak--reproductive biology and isolating mechanisms of Cirrhaea dependens (Orchidaceae).

Floral biology, reproduction, pollinator specificity, and fruit set of Cirrhaea dependens were recorded in forest areas of Southeastern Brazil. Cirrhaea dependens is a lithophytic or epiphytic herb occurring very sparsely below dense canopies. Nearly all the flowers of a single plant open simultaneously before dawn. They are short-lasting and offer floral fragrances as rewards, which are collected by male euglossine bees. Observations carried out in mesophytic forests at Serra do Japi revealed that Euglossa VIRIDIS is their principal pollinator, with Eufriesea violacea a sporadic co-pollinator. Visitation started soon after flower opening, and attractiveness remained high for about 2 h, decreasing abruptly at sunrise. Flower anthesis with subsequent fragrance release seems to be correlated with bee attraction. Observations using chemical baits were carried out at Serra do Japi, and in the Atlantic Rain Forest of Picinguaba. Three euglossine species were captured with pollinaria of C. dependens in Picinguaba, whereas only E. violacea was attracted in Serra do Japi. In Picinguaba, C. dependens occurs sympatrically with C. saccata and C. loddigesii. Each species attracted different pollinators. The specificity and resulting reproductive isolation are due to the production of different odours by each orchid species. Cirrhaea dependens is self-compatible but pollinator-dependent. The reproductive success was low and appears to result from a combination of factors discussed here, such as the production of short-lived flowers, presence of floral mechanisms avoiding self-pollination, non-synchronization of flower phases among plants, and populations with few and sparsely distributed individuals.

Animals↗

PubMed2004

Speciation genes.

Until recently, the genes that cause reproductive isolation remained black boxes. Consequently, evolutionary biologists were unable to answer several questions about the identities and characteristics of "speciation genes". Over the past few years, however, evolutionary geneticists have finally succeeded in isolating several such genes, providing our first glimpse at factors that are thought to be representative of those underlying the origin of species. Evolutionary analysis of these genes suggests that speciation results from positive Darwinian selection within species. Molecular evolutionary study of the genes causing reproductive isolation may represent an important new phase in the study of speciation.

Animals↗

PubMed2004

Evidence for ecology's role in speciation.

A principal challenge in testing the role of natural selection in speciation is to connect the build-up of reproductive isolation between populations to divergence of ecologically important traits. Demonstrations of 'parallel speciation', or assortative mating by selective environment, link ecology and isolation, but the phenotypic traits mediating isolation have not been confirmed. Here we show that the parallel build-up of mating incompatibilities between stickleback populations can be largely accounted for by assortative mating based on one trait, body size, which evolves predictably according to environment. In addition to documenting the influence of body size on reproductive isolation for stickleback populations spread across the Northern Hemisphere, we have confirmed its importance through a new experimental manipulation. Together, these results suggest that speciation may arise largely as a by-product of ecological differences and divergent selection on a small number of phenotypic traits.

Alaska↗

PubMed2005

Species delimitation in native South American fire ants.

The taxonomy of fire ants has been plagued by difficulties in recognizing species on the basis of morphological characters. We surveyed allozyme markers and sequences of the mtDNA COI gene in several closely related nominal species from two areas of sympatry in the native ranges to learn whether the morphology-based delimitation of these species is supported by genetic data. We found that Solenopsis invicta and Solenopsis richteri, pest species whose distinctiveness has been debated, appear to be fully reproductively isolated at both study sites. This isolation contrasts with the extensive hybridization occurring between them in the USA, where both have been introduced. We also found strong genetic differentiation consistent with barriers to gene flow between Solenopsis quinquecuspis and the other two species. However, several lines of evidence suggest that nuclear and mitochondrial genes of S. invicta and S. richteri are introgressing into S. quinquecuspis. The latter apparently is a recently derived member of the clade that includes all three species, suggesting that there has been insufficient time for its full development of intrinsic isolating mechanisms. Finally, our discovery of genetically distinct populations within both S. invicta and S. richteri suggests the presence of previously unrecognized (cryptic) species. Their existence, together with the difficulties in developing diagnostic morphological characters for described species, imply that the group is actively radiating species and that morphological divergence generally does not keep pace with the development of reproductive isolation and neutral genetic divergence in this process.

Animals↗

PubMed2005

Speciation by distance in a ring species.

Ring species, which consist of two reproductively isolated forms connected by a chain of intergrading populations, have often been described as examples of speciation despite gene flow between populations, but this has never been demonstrated. We used amplified fragment length polymorphism (AFLP) markers to study gene flow in greenish warblers (Phylloscopus trochiloides). These genetic markers show distinct differences between two reproductively isolated forms but gradual change through the ring connecting these forms. These findings provide the strongest evidence yet for "speciation by force of distance" in the face of ongoing gene flow.

Adaptation, Biological↗

PubMed2006

Speciation by hybridization in Heliconius butterflies.

Speciation is generally regarded to result from the splitting of a single lineage. An alternative is hybrid speciation, considered to be extremely rare, in which two distinct lineages contribute genes to a daughter species. Here we show that a hybrid trait in an animal species can directly cause reproductive isolation. The butterfly species Heliconius heurippa is known to have an intermediate morphology and a hybrid genome, and we have recreated its intermediate wing colour and pattern through laboratory crosses between H. melpomene, H. cydno and their F1 hybrids. We then used mate preference experiments to show that the phenotype of H. heurippa reproductively isolates it from both parental species. There is strong assortative mating between all three species, and in H. heurippa the wing pattern and colour elements derived from H. melpomene and H. cydno are both critical for mate recognition by males.

Animals↗

PubMed2006

Reproductive swarming of sympatric nereidid polychaetes in an estuary of the Omuta-gawa river in Kyushu, Japan, with special reference to simultaneous swarming of two Hediste species.

Habitat differences and spatial and temporal separation in reproductive swarming among sympatric nereidid polychaetes were examined in an estuary of the Omuta-gawa River, Kyushu, Japan by annual periodical sampling from December 2003 to January 2005. Benthic adults of Tylorrhynchus osawai and Hediste diadroma occupied mainly the upper reaches of the estuary, whereas those of H. japonica usually inhabited the middle reaches, though their distributions overlapped. Reproductive swarming of mature adults occurred in the estuary just after high tide at night during spring tides in four nereidids: H. japonica (in the middle and lower reaches from late December to late February), H. diadroma (throughout the whole estuary from middle December to late April), T. osawai (in the middle reaches and another estuary from late October to late December), and Nectoneanthes oxypoda sensu Imajima, 1972 (in the lower reaches in late April and early May). This result shows that temporal separation of reproductive swarming may act as a reproductive isolation mechanism among these nereidids, except for H. japonica and H. diadroma. Simultaneous swarming and mass-spawning of the two Hediste species were commonly observed in the middle and lower reaches from late December to early February, suggesting the absence of a pre-spawning barrier to reproductive isolation between them. We found no difference in spawning behavior between H. japonica and H. diadroma. Males of both species seemed to participate in swarming earlier than females.

Animals↗

PubMed1975

Mycoplasma hominis: growth, reproduction, and isolation of small viable cells.

Improved methods for studying the growth of Mycoplasma hominis (ATCC 14027) have been developed, involving modified growth conditions and preparation of the organisms under minimally distorting conditions. Cells so prepared from batch cultures show relatively uniform exponential growth and appear to be dividing by binary fission; but pleomorphic forms appear upon further incubation. Similar behavior was demonstrated by another laboratory-adapted strain and by three clinical isolates, and therefore seems characteristic of the species. The pleomorphic populations contain small forms having diameters within the 100- to 250-nm size range reported for "elementary bodies." Such forms were isolated from this strain of M. hominis by sequential filtration using gravity alone, after cell aggregates were dispersed by Pronase treatment. Of the small bodies which traversed membranes of 220-nm pore size, a negligible number grew in liquid or on solid media, suggesting that these were not essential reproductive units in a life cycle, but involution forms due to growth in an altered environment.

Bacteriological Techniques↗

PubMed1999

Inbreeding and cancer incidence in human isolates.

This study investigates the incidence of cancer in isolate populations. Thorough anthropological research over the past 3 decades has established island populations in Middle Dalmatia, Croatia, as outstanding examples of genetic isolates. The number of cancer cases on 5 islands (Brac, Hvar, Korcula, Vis, and Lastovo) over a 20-year period (1971-1990) has been extracted from the data of the Croatian Cancer Registry. The population of coastal Dalmatia, characterized by similar environmental factors but a different population genetic structure, was used as a control population. The leading hypothesis was that, if there were genes or gene complexes (especially with recessive inheritance) responsible for genetic susceptibility to certain types of cancer, then the incidence of those cancer types should be greater in reproductively isolated island populations than in a control population because of increased manifestation of such genes or gene complexes caused by inbreeding. Furthermore, the cancer incidence should increase along with greater reproductive isolation (i.e., greater geographic distance of the islands from the mainland). After adjusting the data for sex and age, I confirmed the hypothesis: Island populations have greater total cancer incidence than the control population for both sexes. The excess incidence on the islands shows an almost linear correlation with geographic distance from the mainland. The cancer sites primarily responsible for the excess incidence are bladder cancer in males, and breast, ovarian, brain, and large bowel cancer in females, predominantly in the younger age groups.

Adult↗

PubMed2006

Placental invasiveness mediates the evolution of hybrid inviability in mammals.

A central question in evolutionary biology is why animal lineages differ strikingly in rates and patterns of the evolution of reproductive isolation. Here, we show that the maximum genetic distance at which interspecific mammalian pregnancies yield viable neonates is significantly greater in clades with invasive (hemochorial) placentation than in clades with noninvasive (epitheliochorial or endotheliochorial) placentation. Moreover, sister species with invasive placentation exhibit higher allopatry in their geographic ranges, suggesting that formerly separated populations in mammals with this placental type fuse more readily on recontact. These differences are apparently driven by the stronger downregulation of maternal immune responses under invasive placentation, where fetal antigens directly contact the maternal bloodstream. Our results suggest that placental invasiveness mediates a major component of reproductive isolation in mammals.

Animals↗

PubMed2004

Random amplified polymorphic DNA fingerprinting as a marker for Paramecium jenningsi strains.

The aim of the present study is to establish a common RAPD marker for P. jenningsi using a series of Ro primers and to investigate if strains originating from distant and isolated localities (Japan, China, India, Saudi Arabia) have isolated gene pools and represent distinct species. An analysis of dendrograms constructed on the basis of RAPD-PCR fingerprints with four primers (Ro 460-04, 460-06, 460-07, and 460-10) from the first part of this project (SKOTARCZAK et al. 2004), assigns the strains to two groups consisting of the continental strains (India, Saudi Arabia, China) and Japanese strains that have been considered as a separate sibling species within P. jenningsi. The genetic similarity of the Indian and Arabian strains was ascertained, whereas the Chinese strain formed an independent branch in this sibling species. The primers Ro (460-01,460-02, 460-03, 460-05, 460-08) also distinguish between two groups of strains, although they divide the Japanese strains into two subgroups that are not reproductively isolated. This probably indicates genetic variation within this sibling species. However, it comprises one common gene pool (successful inter-strain crosses) and is reproductively isolated from the other sibling species. The results presented in these papers confirm that the construction of ten band patterns having marker attributes is possible on the basis of DNA amplification from 9 strains of P. jenningsi with the RAPD-PCR fingerprinting method using five primers from the Ro series. The patterns can be assigned to three marker-groups: a general species group, a group differentiating between sibling species, and accessory strain markers.

Animals↗

PubMed2001

Sexual conflict and evolution in Trinidadian guppies.

Recent investigations have highlighted the importance of sexual conflict in the evolution of reproductive isolation. Examination of the Trinidadian guppy (Poecilia reticulata) shows how geographic variation in sexual conflict can mediate the emergence of isolating mechanisms. On the basis of pre-mating behaviour guppy females appear to be winning the battle of the sexes in low risk localities whereas males are apparently ahead in high-predation environments. However, the conclusion that sexual selection (through female choice) is replaced by sexual coercion of females (as a consequence of sneaky mating) in predator rich (and productive) assemblages takes no account of post-copulatory mechanisms. Recent work on sperm competition in guppies suggests coevolution between males and females may also occur in the post-mating, pre-zygotic arena. The potential for the evolution of reproductive isolation at each stage of the mating sequence is assessed.

Animals↗

PubMed1995

Biological relationships among the Iroquois.

The intrusive cultural and linguistic position of Iroquoian-speaking peoples among Algonquian speakers of the lower Great Lakes region has sparked much debate concerning their cultural and biological origins. Previous physical anthropological studies, largely limited to typological or univariate osteometric analyses, have produced equivocal and contradictory results, offering little insight into the question of origins. This study addresses the question of Iroquois origins by examining biological relationships in the lower Great Lakes region using a multivariate analysis of anthropometric data. The study uses 12 body and head measurements taken on 843 individuals from 7 Iroquoian and 4 Algonquian groups. The data were examined using biodistances, canonical variate analysis, and a model of differential gene flow. The results indicate a possible biological distinction between Iroquoians and Algonquians, suggesting different biological origins. Gene flow in prehistoric and historical times may have mitigated much of this differentiation. The Onondaga most closely approximate the ancestral Iroquoian phenotype and are phenotypic outliers, probably because of reproductive isolation from the Algonquians. The Onondaga have unexpectedly high mean phenotypic variance with respect to distance from the phenotypic centroid, suggesting a greater than average degree of external gene flow. Because no viable source for external genes can be determined, however, the Onondaga's high mean variance may be better explained through patterns of nonrandom mating and reproductive isolation.

Anthropometry↗

PubMed2004

Floral symmetry affects speciation rates in angiosperms.

Despite much recent activity in the field of pollination biology, the extent to which animal pollinators drive the formation of new angiosperm species remains unresolved. One problem has been identifying floral adaptations that promote reproductive isolation. The evolution of a bilaterally symmetrical corolla restricts the direction of approach and movement of pollinators on and between flowers. Restricting pollinators to approaching a flower from a single direction facilitates specific placement of pollen on the pollinator. When coupled with pollinator constancy, precise pollen placement can increase the probability that pollen grains reach a compatible stigma. This has the potential to generate reproductive isolation between species, because mutations that cause changes in the placement of pollen on the pollinator may decrease gene flow between incipient species. I predict that animal-pollinated lineages that possess bilaterally symmetrical flowers should have higher speciation rates than lineages possessing radially symmetrical flowers. Using sister-group comparisons I demonstrate that bilaterally symmetric lineages tend to be more species rich than their radially symmetrical sister lineages. This study supports an important role for pollinator-mediated speciation and demonstrates that floral morphology plays a key role in angiosperm speciation.

Biodiversity↗

PubMed2003

Positive selection in the egg receptor for abalone sperm lysin.

The mechanism of speciation is a central problem in evolutionary biology. In free-spawning animals with no complex mating behavior, prezygotic reproductive isolation (speciation) could result from the rapid divergence of genes coding for sperm and egg proteins that bind each other during fertilization. In abalone, sperm lysin evolves rapidly by positive Darwinian selection. The egg vitelline envelope receptor for lysin had previously been shown to evolve neutrally and be subjected to concerted evolution. Several mathematical simulations predict that both male and female reproductive proteins should evolve rapidly by positive selection. Here we report that the sequence diversity of the amino-terminal end of the egg vitelline envelope receptor for lysin has been promoted by positive Darwinian selection. These data provide molecular support for theoretical models showing that the two sexes are locked in a "coevolutionary chase" that could be driven by processes such as sexual selection, sexual conflict, or microbial attack (pathogen avoidance). The result of this continuous coevolution of the gamete recognition system could be the splitting of one population into two that are reproductively isolated (speciation).

Animals↗

PubMed2006

Two distinct groups of natural populations of Fagopyrum urophyllum (Bur. et Franch.) Gross revealed by the nucleotide sequence of a noncoding region in chloroplast DNA.

Fagopyrum urophyllum is a cross-pollinating perennial woody shrub species belonging to the urophyllum group of Fagopyrum. Natural populations of F. urophyllum were morphologically classified into two distinct groups, the Dali group and the Kunming group without exception. This grouping was verified by molecular phylogeny based on the nucleotide sequence of chloroplast DNA. The reproductive isolation found between the two groups was almost perfect as the distribution of two groups did not overlap each other. The net nucleotide substitution rate (Da) between the two groups was at the same level as between two distinct species. These data suggests that the two groups should be classified into distinct species if future studies on F. urophyllum confirm complete reproductive isolation and no ambiguously classified populations in the border area of the central Yunnan province of China.

DNA, Chloroplast↗

PubMed2006

Linking color polymorphism maintenance and speciation.

Here, we review the recently burgeoning literature on color polymorphisms, seeking to integrate studies of the maintenance of genetic variation and the evolution of reproductive isolation. Our survey reveals that several mechanisms, some operating between populations and others within them, can contribute to both color polymorphism persistence and speciation. As expected, divergent selection clearly can couple with gene flow to maintain color polymorphism and mediate speciation. More surprisingly, recent evidence suggests that diverse forms of within-population sexual selection can generate negative frequency dependence and initiate reproductive isolation. These findings deserve additional study, particularly concerning the roles of heterogeneous visual environments and correlational selection. Finally, comparative studies and more comprehensive approaches are required to elucidate when color polymorphism evolves, persists, or leads to speciation.

Animals↗

PubMed2004

Discriminating males alter sperm production between species.

Prezygotic reproductive isolation and its importance in speciation is traditionally approached from the viewpoint of those events that occur before mating. However, recent interest in sperm competition theory has shown that prezygotic isolation can be affected by mechanisms that occur after mating but before fertilization. One neglected aspect of these studies is how the cost of sperm production might play a role in species isolation. We examined differential sperm production in a species whose males are sexually parasitized by a unisexual gynogenetic species. Gynogens are clonal females that require sperm from males of closely related bisexual species to initiate embryogenesis. We tested for differential sperm production by male sailfin mollies (Poecilia latipinna) when they were in the presence of either a heterospecific, gynogenetic female (Poecilia formosa, Amazon molly) or a conspecific female. We found that previously demonstrated male mate choice for conspecific over heterospecific females also is revealed in sperm production. Males from both an allopatric and a sympatric population produce more sperm when in the presence of a conspecific female than when in the presence of a heterospecific female. We suggest that differential sperm production also could play a role in prezygotic reproductive isolation in bisexual species complexes that occur in sympatry.

Animals↗