×Polascontria (Cactaceae), a nothogenus that represents the gene flow between Escontria and Polaskia

Hybridization represents an important mechanism in the diversification of Cactaceae where interspecific barriers are poorly developed. Putative hybrids with an intermediate phenotype between the columnar cacti Escontria chiotilla and Polaskia chichipe were observed in Oaxaca, Mexico. The putative hybrids grow sympatrically with their parents, sharing pollinators and overlapping flowering periods. On the basis of morphological, genetic and molecular studies, we show that a gene flow occurs between E. chiotilla and P. chichipe. Morphological and genetic similarities were used to carry out phenetic analyses, which allowed us to separate the two taxa and the potential hybrids, and cluster them into discrete groups with a high degree of consistency. We also generate artificial hybrids by hand-pollination crosses. These hybrids indicate that there are partial pre- and postzygotic barriers between E. chiotilla and P. chichipe. Backcrosses between parents and hybrids produced viable seeds, suggesting that there is a high potential of introgression with both parents. Taken together, we propose that hybrids observed in the field are the product of cross-pollination between E. chiotilla and P. chichipe. Thus, gene flow between both genera can explain why the genetic independence of these taxa has not kept them reproductively isolated. A complete description and illustrations of a new intergeneric hybrid are provided.

THE SOCIAL CONTEXT OF CONTACT CALLS BY ROOKS (CORVUS FRUGILEGUS)

Communication is the link between individuals of one species and represents the essence of social life. Vocal communication is one of the most studied forms of information exchange, although it also comes with interspecific barriers that are still tricky to overcome. While we are able to understand the meaning of another human’s words, we fail to understand an animal’s utterances. Among these, bird song has become a field of particular interest. However, little is known yet about many species’ vocalizations, and even less about their significance or how different factors influence them. The presented study establishes the vocal repertoire of a group of rooks and further investigates the importance of contact calls between partners in an experiment. We found that test subjects and other group members produced more contact calls after than before partners had been separated from each other, indicating stress induced by physical isolation and/or the lack of visual contact as an important factor influencing the call frequency. Separating certain individuals seemed to affect the group differently, which indicates that the ‘importance’ of the animal to the group influences the group call rate. In this study, we have shown how social and environmental factors play a role in vocal communication in birds.

THE UNILATERAL INTERSPECIFIC CROSSING BARRIER IN LYCOPERSICON IS NOT SELF INCOMPATIBILITY

Little is known about the mechanisms controlling interspecific barriers, unlike the well studied intraspecific barrier, self incompatibility (SI),. A unilateral crossing barrier (unilateral incongruity - UI) exists among the Lycopersicon species, in which crossing is impeded or prevented in one direction. Since both UI and SI can give unilateral differences in seed set, suggestions have been made that UI and SI are functionally related. L. pennellii LA716 is self-compatible, unlike the other accessions which are SI, but LA716 still exhibits UI with L. esculentum (esc). We observed the development of pollen tubes in self and cross pollinations of LA716, esc and SI accessions of L. pennellii (pen). Selfed pollen tubes in esc were at the ovary in 24 hours, while pen were 1/2 way down the style and in LA716 the pollen had not germinated. By 48 hours, the pollen tubes in LA716 were in the ovary and growth had halted in pen styles. Crosses with LA716 pollen on esc and pen resulted in pollen tube growth starting within 24 hours continuing to the ovary. Thus, UI is not a SI response and LA716 shows a delayed pollen germination and growth unlike the other Lycopersicon species examined.

THE NATURE AND MEANS TO OVERCOME HYBRID BREAKDOWN IN THE F2 OF AN INTERSPECIFIC CROSS IN LYCOPERSICON

The transfer of multigenic traits into tomato has been slow due to interspecific barriers (hybrid breakdown) found in the F2 of the Lycopersicon esculentum × L. pennellii cross (esc × pen), including blocks in normal reproductive development and nonfecundity. In a typical (esc × pen) F2 population, failure to flower and premeiotic blocks in pollen development occurred in 2% and 11% of the population, respectively. The remaining plants showed a mean of 37% stainable pollen. Twenty three percent of the F2 plants set seed, with an average of 4.5 seeds/fruit. An average of 33% of the stainable pollen from the 7 F2 plants with the highest stainable pollen measurements germinated in vitro, but only 4 of these 7 plants set seed. Thus, percent stainable pollen is not an adequate predictor of fecundity, and the non-fecundity in the F2Le plants must involve barriers occurring after pollen germination.A method was developed which greatly reduces or eliminates each of the F2 barriers. The method and its efficacy on each of the aspects of hybrid breakdown will be discussed.