5,548 research outputs found
Mating Patterns and Post-Mating Isolation in Three Cryptic Species of the Engystomops Petersi Species Complex
Determining the extent of reproductive isolation in cryptic species with dynamic geographic ranges can yield important insights into the processes that generate and maintain genetic divergence in the absence of severe geographic barriers. We studied mating patterns, propensity to hybridize in nature and subsequent fertilization rates, as well as survival and development of hybrid F1 offspring for three nominal species of the Engystomops petersi species complex in YasunĂ National Park, Ecuador. We found at least two species in four out of six locations sampled, and 14.3% of the wild pairs genotyped were mixed-species (heterospecific) crosses. We also found reduced fertilization rates in hybrid crosses between E. petersi females and E. âmagnusâ males, and between E. âmagnusâ females and E. âselvaâ males but not in the reciprocal crosses, suggesting asymmetric reproductive isolation for these species. Larval development times decreased in F1 hybrid crosses compared to same species (conspecific) crosses, but we did not find significant reduction in larval survival or early metamorph survival. Our results show evidence of post-mating isolation for at least two hybrid crosses of the cryptic species we studied. The general decrease in fertilization rates in heterospecific crosses suggests that sexual selection and reinforcement might have not only contributed to the pattern of call variation and behavioral isolation we see between species today, but they may also contribute to further signal divergence and behavioral evolution, especially in locations where hybridization is common and fertilization success is diminished
Mating Patterns and Post-Mating Isolation in Three Cryptic Species of the Engystomops Petersi Species Complex
Determining the extent of reproductive isolation in cryptic species with dynamic geographic ranges can yield important insights into the processes that generate and maintain genetic divergence in the absence of severe geographic barriers. We studied mating patterns, propensity to hybridize in nature and subsequent fertilization rates, as well as survival and development of hybrid F1 offspring for three nominal species of the Engystomops petersi species complex in YasunĂ National Park, Ecuador. We found at least two species in four out of six locations sampled, and 14.3% of the wild pairs genotyped were mixed-species (heterospecific) crosses. We also found reduced fertilization rates in hybrid crosses between E. petersi females and E. âmagnusâ males, and between E. âmagnusâ females and E. âselvaâ males but not in the reciprocal crosses, suggesting asymmetric reproductive isolation for these species. Larval development times decreased in F1 hybrid crosses compared to same species (conspecific) crosses, but we did not find significant reduction in larval survival or early metamorph survival. Our results show evidence of post-mating isolation for at least two hybrid crosses of the cryptic species we studied. The general decrease in fertilization rates in heterospecific crosses suggests that sexual selection and reinforcement might have not only contributed to the pattern of call variation and behavioral isolation we see between species today, but they may also contribute to further signal divergence and behavioral evolution, especially in locations where hybridization is common and fertilization success is diminished
John Tilsed (1747â1834): Servant of George Cartwright and the Slades, Planter of Shoe Cove, Gentleman of Dorset
The effectiveness of protocols when pre-service teachers engage in online collaborations: An exploration
Graduate teachers in Australia are expected to engage with their peers to expand their professional learning. Learning to use protocols â or structured professional conversations â provides pre-service teachers with opportunities to achieve this expectation. In this paper we explain how pre-service teachers during an extended practicum used protocols to participate in synchronous online discussions using the Blackboard Collaborate learning platform. The pre-service teachers were surveyed about aspects of the protocols and the platform on which the interactions occurred. Protocols appear to be well-suited to assisting synchronous discussions using Web 2 technologies as they ensure everyone has equal time to discuss, present and receive feedback about their work in respectful and efficient ways. This preliminary research provides opportunities for further investigation of pedagogical approaches to use with pre-service teachers when they are required to utilise online platforms when they are away from the university for extended periods of time
Badges and rainbow matchings
Drisko proved that matchings of size in a bipartite graph have a
rainbow matching of size . For general graphs it is conjectured that
matchings suffice for this purpose (and that matchings suffice when
is even). The known graphs showing sharpness of this conjecture for even
are called badges. We improve the previously best known bound from to
, using a new line of proof that involves analysis of the appearance of
badges. We also prove a "cooperative" generalization: for and ,
any sets of edges, the union of every of which contains a matching
of size , have a rainbow matching of size .Comment: Accepted for publication in Discrete Mathematics. 19 pages, 2 figure
Modulation of Negative Index Metamaterials in the Near-IR Range
Optical modulation of the effective refractive properties of a "fishnet"
metamaterial with a Ag/Si/Ag heterostructure is demonstrated in the near-IR
range and the associated fast dynamics of negative refractive index is studied
by pump-probe method. Photo excitation of the amorphous Si layer at visible
wavelength and corresponding modification of its optical parameters is found to
be responsible for the observed modulation of negative refractive index in
near-IR.Comment: 11 figures, 4 figure
Cooperative conditions for the existence of rainbow matchings
Let , and let be a family of non-empty sets of
edges in a bipartite graph. If the union of every members of
contains a matching of size , then there exists an -rainbow
matching of size . Upon replacing by , the result can be
proved both topologically and by a relatively simple combinatorial argument.
The main effort is in gaining the last , which makes the result sharp
Wnt/β-Catenin Signaling Pathway Is Necessary for the Specification but Not the Maintenance of the Mouse Retinal Pigment Epithelium
β-Catenin (Ctnnb1) has been shown to play critical roles in the development and maintenance of epithelial cells, including the retinal pigment epithelium (RPE). Ctnnb1 is not only a component of intercellular junctions in the epithelium, it also functions as a transcriptional regulator in the Wnt signaling pathway. To identify which of its functional modalities is critically involved in mouse RPE development and maintenance, we varied Ctnnb1 gene content and activity in mouse RPE lineage cells and tested their impacts on mouse eye development. We found that a Ctnnb1 double mutant (Ctnnb1dm), which exhibits impaired transcriptional activity, could not replace Ctnnb1 in the RPE, whereas Ctnnb1Y654E, which has reduced affinity for the junctions, could do so. Expression of the constitutively active Ctnnb1âex3 mutant also suppressed the development of RPE, instead facilitating a ciliary cell fate. However, the post-mitotic or mature RPE was insensitive to the loss, inactivation, or constitutive activation of Ctnnb1. Collectively, our results suggest that Ctnnb1 should be maintained within an optimal range to specify RPE through transcriptional regulation of Wnt target genes in the optic neuroepithelium.</p
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