This between-forest crossing effect was consistent between types regardless of the higher interspecific difference in dispersal potential. For both kinds, version from inside the fruit lay certainly maternal trees are the very least towards between-tree crosses, suggesting a universal bad interfertility between woods going on in separate tree supplies.
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Mechanisms underlying outbreeding depression may be of a genetic or an ecological nature (Price and Waser, step step 1979; Shields, 1982). Outbreeding depression involving between-population crosses is most often ascribed to the genetic mechanism involving disruption of coadapted gene complexes (Templeton, 1986). According to this model, intrinsic coadaptation involving relatively few loci develops through restricted gene flow among populations and genetic drift within populations (Templeton, 1981; Schierup and Christiansen, 1996). Crossing disparate genomes results in outbreeding depression through the disruption of coadaptation between homologous chromosomes in the F1 generation and between coadapted portions of individual chromosomes in F2 progeny. The outbreeding depression observed in this study, which was restricted to between-forest crosses over 12- and 35-km distances, may be explained in part by disruption of intrinsic coadaptation. The observation of hybrid vigor in seedlings of Sh. cordifolia is also consistent with this model (Templeton, 1986; see below).
In contrast, the ecological mechanism for outbreeding depression involves reduced fitness of wide outcrosses due to adaptation to local biotic and abiotic conditions, such that wide outcrossing yields F1 progeny with alleles maladapted to either of the parental environments (Endler, 1977). Although selection-driven divergence is typically associated with intrapopulation outbreeding depression (e.g., Waser and Price, 1989), selection-driven divergence between populations seems a plausible contributor to the reduced interfertility between populations observed in this study. Through direct selection on fitness traits, habitat heterogeneity will promote genetic differentiation within and among plant populations (Jain and Bradshaw, 1966; Linhart and Grant, 1996). The considerable environmental heterogeneity of southwest Sri Lanka is likely sufficient to cause genetic differentiation of tree populations over a scale of tens of kilometers. The ridge and valley system of southwest Sri Lanka comprises elevations ranging from 300 m to >1000 m. Across elevations, variation in temperature, cloudiness, and rainfall (<2500–5000 cm) occurs (Gunatilleke et al., 1998).
The latest obvious outbreeding despair seen in fresh fruit place and you may cumulative fitness to own ranging from-forest crosses in both kinds implies some degree regarding hereditary isolation certainly forest populations occupying brand new separate tree supplies of Sri Lanka’s damp region. It outcome is slightly stunning considering the large stature of your types and also the small geographic area on it, therefore shows that requirements positive for speciation inside the tropical woods can get occur more a measure from just several to help you tens out of miles. The geographical heterogeneity away from southwestern Sri Lanka, although not, could be out-of a thin scale than simply compared to the majority out of warm forested landscapes (Ashton and you will Gunatilleke, 1987). It will be preferred by see whether bad cross-virility between woods is common for tree varieties about moist region. Unfortunately, intentions to continue this data for the 1998, and to are most other species of Syzygium and you will Shorea, was in fact thwarted because of a broad decreased flowering on area one year. From a preservation direction, observation of even minor reproductive separation ranging from tree supplies shows that also where tree varieties is common certainly supplies, for every forest signifies one hereditary financing really worth conservation.
Outbreeding anxiety was not seen during the crosses over what exactly is allegedly the typical range of pollen disperse to possess possibly species. The possible lack of proof of outbreeding anxiety inside persisted-tree communities within analysis try consistent with the literature inside the hence types of ranging from-population outbreeding despair inside the herbs far outnumber that from in this-inhabitants outbreeding depression. Given the current characteristics out-of deforestation north of Sinharaja, but not, delineation of S. rubicundum into the separate communities on the Sinharaja and you will Walankanda Reserves may maybe not accurately reflect the fresh current market reputation of which kinds. Walankanda and you can Sinharaja Supplies had been part of you to definitely persisted forest until just 29–40 year back (P. S. Ashton, individual telecommunications, Harvard University). That is most likely below the brand new generation time for these types of trees and you will means the opportunity of latest hereditary connections between the two populations. rubicundum are limited to middle-mountain section, not, odds are which species was not found in variety on valley anywhere between Sinharaja and you will Walankanda Reserves prior to the clearing out-of tree because city (P. S. Ashton, personal telecommunications, Harvard School). It doesn’t matter, the two woods was broke up today by an excellent deforested voglio recensione sito incontri cavallerizzi strip simply 4 kilometres wider. Gene move anywhere between tree populations occupying such forests given that separation was hence at the least probable (age.grams., Light, Powell, and you can Boshier, 1998). For these reasons, observation out-of outbreeding anxiety in the crosses ranging from forest populations consuming Sinharaja and Walankanda Reserves is actually unanticipated, also it demonstrates that genetic divergence regarding tree communities can occur more than short distances even in proceeded habitat.