No abstract

Current rates of climate change require organisms to respond through migration, phenotypic plasticity, or genetic changes via adaptation. We focused on questions regarding species' and populations' ability to respond to climate change through adaptation. Specifically, the role adaptive introgression, movement of genetic material from the genome of 1 species into the genome of another through repeated interbreeding, may play in increasing species' ability to respond to a changing climate. Such interspecific gene flow may mediate extinction risk or consequences of limited adaptive potential that result from standing genetic variation and mutation alone, enabling a quicker demographic recovery in response to changing environments. Despite the near dismissal of the potential benefits of hybridization by conservation practitioners, we examined a number of case studies across different taxa that suggest gene flow between sympatric or parapatric sister species or within species that exhibit strong ecotypic differentiation may represent an underutilized management option to conserve evolutionary potential in a changing environment. This will be particularly true where advanced-generation hybrids exhibit adaptive traits outside the parental phenotypic range, a phenomenon known as transgressive segregation. The ideas presented in this essay are meant to provoke discussion regarding how we maintain evolutionary potential, the conservation value of natural hybrid zones, and consideration of their important role in adaptation to climate.

Interspecific hybridization may enhance the capacity of populations to adapt to changing environments, and has practical implications for reforestation. We use genome-wide estimates of admixture and phenotypic traits for trees in a common garden to examine the extent and direction of gene flow across a Picea hybrid zone, testing assumptions of the bounded hybrid superiority and tension zone models of hybrid zone maintenance. Seeds were collected from the ecological transition zone spanning from maritime to continental climates across the Picea sitchensis-P. glauca contact zone, and 721 trees were planted in a common garden experiment within the hybrid zone. Individuals were genotyped using a panel of 384 candidate-gene single nucleotide polymorphisms (SNPs) putatively associated with adaptive traits in Picea, and phenotyped at age ten for height and autumn cold hardiness. Low interspecific heterozygosity in hybrids indicated that intrinsic reproductive barriers were too weak to prevent widespread recombination, although introgression appeared asymmetric with P. sitchensis dominating the zone. Whereas marker-based hybrid index was strongly correlated with climate and geography, phenotypic traits exhibited weak or no significant clines. Our results indicated that exogenous selection appeared to play a strong role in the distribution and structure of this hybrid zone, indicative of an environmentally determined bounded hybrid superiority model of hybrid zone maintenance, although endogenous mechanisms could not be ruled out. This study provides insight into the mechanisms underlying adaptation across ecologically transitional hybrid zones that will ultimately provide an additional tool in managing these economically important tree species.

Two hundred and fifty-nine patients with mucosal melanoma of the head and neck were reviewed. The data of these patients were obtained from the records of the Department of Head and Neck Oncology at the University of Liverpool and from the Merseyside and Cheshire Cancer Registry. Survival curves were constructed using the life table method and differences were investigated by the Log Rank Test. Prognostic factors were further analysed by Cox's proportional hazards model. Melanomas of the nasal cavities and sinuses accounted for 69%; 22% occurred in the oral cavity and 9% in the pharynx, larynx and upper oesophagus. In 49% treatment was by wide local resection and in 8% by irradiation. Thirty-six per cent had combined modalities of treatment. Primary site recurrence occurred in 52% and 36% developed nodal recurrence. The tumour specific survival at 5 years was 45% at 10 years 28%, at 20 years 17% and closely resembled the observed survival. Young male patients tended to have a favourable prognosis as did those treated surgically. Radiotherapy on its own was ineffective. Amelanotic melanoma had a particularly poor survival. Whereas site had no effect on survival. The study confirms the poor prognosis of mucosal melanoma of the head and neck. Young patients should be offered radical surgical treatment combined with radical radiotherapy if feasible as this offers the best chance of cure.