LOCI AFFECTING LONG-TERM HYBRID SURVIVORSHIP IN LOUISIANA IRISES: IMPLICATIONS FOR REPRODUCTIVE ISOLATION AND INTROGRESSION

Abstract

Iris fulva and I. brevicaulis are long‐lived plant species known to hybridize where they coexist in nature. Year‐to‐year survival contributes significantly to overall fitness for both species and their hybrid derivaties, and differences in hybrid survivability may have improtant consequences to interspecific gene flow in nature. We examined the genetic archiecture of long‐term survivorship of reciprocal backcross I.fulva X I.brevicaulis in a commongarden, greenhouse environment. Differences in mortality were found between the two backcross (BC1)hybrid classes, with hybrids crossed toward I.fulva (BCIF)revealing twice the mortality of those hybrids backcrossed toward I. brevicaulis (BCIB). Using genomic scans on two separate genetic linkage maps derived from the reciprocal hybrid populations, we found that hybrid survivorship is influenced by several genetic regions. Multiple interval mapping (MIM)revealted four quantitative trait loci(QTLs) in BCIF hybrids that were significantly associated with sruvivorship. Introgressed I. brevicaulis DNA increased survivorship at three of the four QTLs. For the fourth QTL, introgressed I.brevicaulis DNA was associated with decreased survivorship. No QTLs were detected in BCIB hybrids; however, single marker analysis revealed five unlinked loci that were significantly associated with survivorship. At all five markers, survivorship was positively associated with introgressed I.fulva DNA. The present dindings have important implications for the evolutionary dynamics of naturally occurring hybrid zones. Regions of the genome that imcrease survivorship when in a heterozygous (i.e., hybrid) state should have an increased likelihood of passing across species boundaries, whereas those that decrease survivoship will be less likely to introgress.