Comparative genetic structure of two co-occurring tree species, Maclura pomifera (Moraceae) and Gleditsia triacanthos (Leguminosae)

Abstract

Mac/urn potnifera, an aulotetraploid, and Gleditsia triacanthos, a diploid, are ecologically similar dioecious tree species that often co-occur in early successional habitats throughout the mid-western United States. We studied levels of genetic diversity and patterns of genetic structure for four polymorphic enzyme lcd of M. pomifera and 16 polymorphic enzyme loci of C. triacanthos from a single population in eastern Kansas. Levels of expected heterozygosity were high for both species, averaging 0.725 for M. poinifera and 0.366 for G. triacanthos. Although genotypes for nearly all G. niacanthos loci were in Hardy-Weinberg frequencies, three of four M. pomifera loci deviated from equilibrium expectations. Two aspects of genetic structure were explored. First, the extent of clonal growth was estimated by comparing genotypes of stems within 50 G. triacanthos and 32 M. poinifera clumps. The great majority of clumps contained more than one genotype, and in many clumps, all stems were genetically unique. Secondly, as revealed by spatial autocorrelation analyses, genetic substructure was very local for both species, with significant positive autocorrelation occurring only within clumps of individuals or among near neighbours. We argue that this pattern of spatial structure for both species results from extremely local seed dispersal and establishment of individuals from the same multiseeded fruit.

Space-time patterns of genetic structure within a stand of Androcymbium gramineum (Cav.) McBride (Colchicaceae)

“…Consistently, most studies involving large populations have elicited patterns of spatial genetic organization over short distances (Epperson & Clegg, 1986;Schoen & Latta, 1989;Perry & Knowles, 1991;Schnabel et at., 1991;Wagner et a!., 1991;Shapcott, 1995), although some exceptions seem to occur (Levin, 1976;Dewey & Heywood, 1988). The existence of spatial structuring in large populations facilitates the generation and maintenance of high levels of variability with which to sustain efficient reproductive performance, survive stochastic events or adjust to novel fluctuating environments (Huenneke, 1991).…”

“…Plant populations can manifest different patterns of genetic structure owing to a variety of demographic and life history traits (Levin & Kerster, 1974;Antonovics & Levin, 1980;Schnabel et at., 1991). From a general point of view, the genetic structure of natural populations can be conceived as the organization of variability emerging from the continued interaction between ecological conditions and historical contingency.…”

Allozyme variation and structure of the Canarian endemic palm tree Phoenix canariensis (Arecaceae): implications for conservation

“…Allozyme polymorphisms have provided valuable data to assess the genetic variability of endemic species (Allphin et al, 1998;Godt and Hamrick, 1998;Batista et al, 2001), and their population genetic structuring (Schnabel et al, 1991;Shapcott, 1995;Caujapé-Castells et al, 1999). They have also been used successfully to characterise and differentiate close by related species, ecological varieties or natural and artificial hybrids (Rieseberg et al, 1989;Booij et al, 1995;Bendiab et al, 1998;Elisiário et al, 1999).…”

Estrutura genética espacial em populações naturais de Machaerium villosum Vog. (Leguminosae) na região de Moji-Guaçu, SP, Brasil

“…Os estudos sobre a estrutura genética espacial de populações de plantas têm revelado padrões diferenciados. Há os que obtém estruturação moderada em faixas curtas de distância e atribuem tal fato à dispersão limitada de pólen e sementes, à reprodução vegetativa e à seleção variando espacialmente (Perry & Knowles 1991, Schnabel et al 1991, Loiselle et al 1995, Shapcott 1995. Há estudos que não encontraram evidências de estruturação (Leonardi & Menozzi 1996, Doligez & Joly 1997.…”

“…Sokal & Oden (1978b) dão um exemplo de união de diferentes estágios de vida em uma mesma análise, não sendo prejudicadas as conclusões, antes o contrário, o padrão de distribuição dos diferentes estágios pôde explicar determinadas estruturações. Há ainda, estudos que utilizam árvores maduras (Perry & Knowles 1991, Schnabel et al 1991, Leonardi & Menozzi 1996, sem especificar o estágio dos indivíduos e trabalhos que utilizam somente árvores adultas (Loiselle et al 1995, Doligez & Joly 1997. Epperson & Alvarez-Buylla (1997) analisam três estágios diferentes de vida (plântulas, juvenis e adultos) de uma espécie arbórea pioneira tropical, porém, o fazem separadamente.…”