Genomic alterations in the interspecific hybrid Helianthus annuus×Helianthus tuberosus

 The genome of a Helianthus annuus (2n=34) ×Helianthus tuberosus (2n=102) hybrid was studied at cytological, biochemical and molecular levels and compared to those of the parental species. Cytophotometric analyses showed that the hybrid has a 4C DNA content higher than expected and with a larger variability than in the parents. This high variability is probably not related to chromosome-number variations since the hybrid always had 2n=68 chromosomes. Moreover, hybrid interphase nuclei showed lower heterochromatin condensation than the parental ones. Thermal denaturation of genomic DNAs indicated that quantitative variation of some DNA families occurred in the hybrids compared to parents. Finally, molecular analyses of DNAs restricted with different enzymes, after Southern blotting and hybridization with HR probes, showed restriction patterns in the hybrid different from those observed in parents. These results indicate that interspecific hybridization between H. annuus and H. tuberosus may determine quantitative variation of some DNA families and differential DNA methylations that probably modify the nuclear structure. These phenomena are probable responses to a “genomic shock” following the interspecific cross. Received: 22 May 1998 / Accepted: 4 June 1998     

Food searching decisions in four cyprinid species

Synopsis Four species of cyprinids (vimba, bream, Danubian bleak and roach) which had been incubated and reared under identical conditions differed qualitatively as well as quantitatively in the use of prey search strategies during comparative experiments. While bream and vimba prefer to use sampling techniques under conditions of reduced visibility of benthic prey, roach favor almost exclusively directed search methods. Vimba and Danubian bleak, in contrast to bream and roach, rapidly increase their total search activity in response to successive presentations of novel prey. These results have several ecological implications which are confirmed by field data. It is concluded that food searching cyprinids follow decision rules which are species specific both in the amount of sampling and in the responsiveness to rapidly changing conditions.     

Host selection in insects: reproductive interference shapes behavior of ovipositing females

In nature, closely related species often utilize different host species, but it is still unclear what factors contribute to the evolution and maintenance of such diversified host selection. In this review, I describe how negative interspecific mating interactions (reproductive interference) can shape host selection by animals, focusing mainly on phytophagous and predatory insects. First, I explain an important premise of this hypothesis, which is that the adult reproductive site is the same as the feeding site for the offspring. Next, I describe several mathematical models and well-studied empirical systems to show that reproductive interference can sufficiently drive and maintain different host selection between phylogenetically related species. Then, I argue for the first time that reproductive interference can cause an oviposition preference in insects that is not optimal for the survival and development of the offspring, as a result of maternal adaptive behavior that maximizes the mother's own fitness. Furthermore, I argue that in insects, reproductive interference probably shapes oviposition behavior before the female alights on the host (e.g., habitat preference), without affecting post-alighting decision making. I would like to emphasize that these two arguments represent the novel approach to clarify the unrevealed pattern of complex insect oviposition behavior.     

The use of IAA to overcome interspecific hybrid inviability in reciprocal crosses between Nicotiana tabacum L. and N. repanda Willd.

Summary Flowering hybrid plants were obtained from reciprocal crosses between N. tabacum L. (2n=48) and N. repanda Willd. (2n = 48), in which cross incompatibility and hybrid inviability were manifested. Stylar pollination and ovule culture were used to overcome the cross incompatibility of stylar barriers and ovular death. It was shown that application of 2 mg/l indole-3-acetic acid (IAA) during the growth period, from the fiveto six-leaf stage to the flowering stage, is a useful and easy method to overcome hybrid inviability.     

Genetic characterization and relationships of Populus alba,P. tremula,and P. x canescens,and their clones

Summary Isozyme analysis was conducted on individuals of Populus alba L., P. tremula L., and P. × canescens Smith to genetically characterize and differentiate species, hybrids, and individuals, and to determine genetic relationships among them. Thirty gene loci, with 71 alleles, coding for 15 enzymes were observed. Individuals could be identified on the basis of their multilocus genotypes. There were 21 unique multilocus genotypes among 23 P. alba clones. Five P. alba clones from Canada were genetically distinct from each other. Each of the 18 P. tremula and 15 P. × canescens clones had unique multilocus genotypes. Thirteen clones had a unique genotype at a single locus. Percentage of polymorphic loci, average number of alleles per locus, and mean observed heterozygosity were, respectively, 50.0, 1.86, and 0.085 in P. alba, 51.7, 1.66, and 0.096 in P. tremula, and 51.7, 1.86, and 0.157 in P. × canescens. Populus alba and P. tremula were genetically distinct from each other and could be distinguished by mutually exclusive alleles at Aco-3, P. tremula-specific gene Mdh-3, and allele frequency differences at 6 loci. Populus × canescens had allele contributions of P. alba and P. tremula. However, their allele frequencies were closer to those of P. alba than being truly intermediate. The mean genetic identity was 0.749 between P. alba and P. tremula, 0.987 between P. alba and P. × canescens, and 0.817 between P. tremula and P. × canescens. Canonical discriminant analysis of multilocus genotypes separated P. alba, P. tremula, and P. × canescens into three distinct groups and portrayed similar interspecific relationship as above. Our results suggested that the putative P. × canescens individuals consisted of a mixture of F₁ hybrids of P. alba and P. tremula and their backcrosses to P. alba.Presently with the University of Alberta, and BioGenetica Inc., P.O. Box 8261, Edmonton, Alberta, Canada T6H 4P1     

Conflicting intersexual mate choices maintain interspecific sexual interactions

Reproductive interference, interspecific sexual interactions that affect reproductive success, is found in various taxa and has been considered as a fundamental source of reproductive character displacement (RCD). Once RCD has occurred, persistent interspecific sexual interactions between species pairs are expected to diminish. However, reproductive interference has been reported from some species pairs that sympatrically coexist. Thus, the question arises, can reproductive interference persist even after RCD? We modeled the evolutionary dynamics of signal traits and mate recognition that determine whether interspecific sexual interactions occur. Our models incorporate male decision making based on the recognition of signal traits, whereas most previous models incorporate only female decision making in mate selection. Our models predict the following: (1) even when male decision making is incorporated, males remain promiscuous; (2) nevertheless, the frequency of interspecific mating is maintained at a low level after trait divergence; (3) the rarity of interspecific mating is due to strict female mate recognition and the consequent refusal of interspecific courtship by females; and (4) the frequency of interspecific mating becomes higher as the cost to females of refusing interspecific courtship increases. These predictions are consistent with empirical observations that males of some species engage in infrequent heterospecific mating. Thus, our models predict that reproductive interference can persist even after RCD occurred.     

No competition for resources between two tick species at their parapatric boundary

Summary Aponomma hydrosauri and Amblyomma limbatum are tick species with the same major host species, the sleepy lizard Trachydosaurus rugosus, but parapatric distributions in South Australia. Near Mt. Mary one species is abruptly replaced by the other over one kilometre. There is substantial overlap in feeding sites on the hosts. This suggested that interspecific competition, during feeding, may be an important mechanism preventing further overlap of the distributions of the two species. However, in the overlap region there was no resource shortage, and each species infested hosts independently of the other species. Also in laboratory experiments at the highest densities encountered in the field, larvae and nymphs of each species attached and engorged equally well whether alone or mixed with the other species. These data refuted the, hypothesis of interspecific competition between the two species while feeding.     

Does heterospecific seminal fluid reduce fecundity in interspecific copulation between seed beetles?

Reproductive interference through mating between related species can cause fitness reduction and affect population dynamics of the interacting species. In experimental matings between two seed beetles, Callosobruchus chinensis and Callosobruchus maculatus, C. maculatus females, but not C. chinensis females, suffer from significant loss of fecundity when conspecific mating is followed by heterospecific mating. We hypothesized that male traits associated with sexual conflict, which are often harmful to females, pleiotropically affect fitness of heterospecific females through interspecific mating. We examined the effect of ejaculate of C. chinensis males on C. maculatus females as the cause of the fecundity loss in C. maculatus females due to interspecific copulation. We found that frequent interspecific copulation occurred between C. maculatus females and C. chinensis males, but not between C. chinensis females and C. maculatus males, resulting in frequent interspecific ejaculate transfer from C. chinensis males to C. maculatus females. However, injection of the extract from C. chinensis male reproductive organs into C. maculatus females did not significantly affect C. maculatus fecundity compared with saline injection, indicating that the effect of the heterospecific ejaculate transfer on fecundity is negligible. We suggest that other harmful male traits such as genital spines of C. chinensis males are mainly responsible for the fecundity reduction in C. maculatus females that have experienced interspecific mating.     

Instability of non-constant equilibrium solutions of a system of competition-diffusion equations

The system of interaction-diffusion equations describing competition between two species is investigated. By using a version of the Perron-Frobenius theorem of positive matrices generalized to function spaces, it is proved that any non-constant equilibrium solution of the system is unstable both under Neumann boundary conditions (for the rectangular parallelepiped domain) and under periodic conditions. It is conjectured that this result extends to convex domains, and that the simple interaction-diffusion model cannot explain spatially segregated distributions of two competing species in such domains.