That it anywhere between-forest crossing impression try consistent ranging from types inspite of the higher interspecific difference between dispersal potential. For both variety, variation into the fresh fruit place certainly one of maternal trees is actually minimum into between-forest crosses, recommending a beneficial common poor interfertility between woods taking place into the independent tree reserves.
Mechanisms underlying outbreeding depression may be of a genetic or an ecological nature (Price and Waser, 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. , 1998).
The newest noticeable outbreeding despair seen in fruits lay and you may cumulative physical fitness to own anywhere between-tree crosses both in species implies a point regarding hereditary isolation among forest populations consuming the fresh new independent forest supplies out-of Sri Lanka’s moist zone. That it outcome is slightly surprising because of the large stature of one’s varieties and also the small local area inside, therefore suggests that requirements favorable to own speciation within the warm woods can get arise more a size from just multiple so you’re able to tens from kilometers. New geographic heterogeneity of southwest Sri Lanka, not, tends to be off a thin size than simply that the majority out-of tropical forested surface (Ashton and you may Gunatilleke https://datingranking.net/fr/rencontres-nudiste/, 1987). It will be desirable to determine whether poor mix-fertility anywhere between forests try common getting tree types about damp zone. Unfortunately, plans to continue doing this investigation for the 1998, also to were most other types of Syzygium and you will Shorea, had been thwarted due to a standard decreased blooming from the part one to year. Regarding a preservation angle, observance regarding actually minor reproductive isolation anywhere between tree reserves signifies that even where tree variety was common one of reserves, for each and every tree means a singular genetic resource really worth conservation.
Across elevations, variation in temperature, cloudiness, and rainfall (<2500–5000 cm) occurs (Gunatilleke et al
Outbreeding anxiety was not imagined in the crosses more than what’s allegedly the normal a number of pollen flow to possess either varieties. The lack of proof of outbreeding despair contained in this continuing-tree populations inside research try similar to the books during the and therefore types of anywhere between-populace outbreeding anxiety when you look at the plants far outnumber the ones from within-populace outbreeding depression. Because of the present nature out-of deforestation north out of Sinharaja, but not, delineation out-of S. rubicundum toward independent populations on the Sinharaja and you will Walankanda Supplies could possibly get not truthfully mirror the brand new recent market reputation of so it kinds. Walankanda and you can Sinharaja Reserves had been element of that continuous forest up to just 29–forty year ago (P. S. Ashton, private communication, Harvard College or university). This will be most likely below the fresh new age group returning to such woods and you will ways the opportunity of present genetic connectivity between the two populations. Because S. rubicundum could be simply for mid-mountain components, not, it is likely that which types wasn’t found in variety about valley anywhere between Sinharaja and you may Walankanda Supplies before the cleaning from tree for the reason that urban area (P. S. Ashton, personal communication, Harvard College). No matter, the two forests is actually split today from the a great deforested remove only 4 kilometer broad. Gene disperse ranging from forest communities occupying these woods due to the fact separation try therefore at the very least plausible (age.g., White, Powell, and Boshier, 1998). Hence, observation regarding outbreeding despair from inside the crosses between tree populations occupying Sinharaja and Walankanda Reserves are unforeseen, plus it indicates that genetic divergence out-of tree populations may appear more than short distances even yet in carried on environment.