Plant hybrids in the wild: evidence from biological recording

Abstract

Although plant hybrids are under‐recorded by botanists, the hybrids of Britain and Ireland are as well known as those of any comparable area. Of the 909 accepted hybrids, 301 have at least one alien parent and these include 152 taxa that have been introduced to the wild (usually from horticultural sources) as hybrids. The parental distributions of the spontaneous hybrids are described as either nested or overlapping; some of the most remarkable hybrids have parents with contrasting European distributions that overlap very narrowly. There are few annual or biennial hybrids and they tend to be sterile and closely associated with the parents, except for numerous annual Euphrasia hybrids. Perennial hybrids with moderate fertility or the capacity for vegetative reproduction are recorded on average from more hectads than sterile, non‐clonal perennials and some show considerable independence of their parental distributions. This independence may result from the decline of one parent or the spread of the hybrid; in many cases the explanation is unknown. Molecular methods have made invaluable contributions to our knowledge of some hybrids in recent years, but universal identification tools cannot currently be applied to plant hybrids so progress with such studies is likely to be piecemeal and slow.

Hybridization and hybrid speciation under global change

“…For example, in the flora of the British Isles, c . 17% (152 of 909) of hybrids were introduced as hybrids (Preston & Pearman, ). Moreover, some of these are deliberate introductions of hybrids of agricultural or horticultural interest such as Mentha (Lamiaceae), Mimulus (Phrymaceae), and Verbascum (Scrophulariaceae).…”

“…When sexual reproduction is severely impaired, asexual reproduction can allow individuals to persist and spread (Grant, ). In the British Isles, perennial hybrids that can propagate through clonal reproduction are more widespread than those that cannot (Preston & Pearman, ; Table ), showing that the capacity for vegetative reproduction is correlated with spatial coverage. Furthermore, analysis of introduced taxa in the recently published alien flora of the British Isles (Stace & Crawley, ) indicates that c .…”

“…Whether the incidence of hybridization at a global scale is changing, and if so at what rate, is still unclear, yet analyses of well‐studied floras, such as that of the British Isles, indicate that a significant fraction of hybrid taxa may involve introduced taxa (Stace & Crawley, ; Stace et al ., ). Among the flora of Britain and Ireland, hybridization involving introduced (nonnative) taxa is well documented (Stace et al ., ; Stace & Crawley, ; Table ), and a recent survey revealed that 33% of hybrid taxa (301 of 909) involve introduced (nonnative) taxa (Preston & Pearman, ). Approximately half of these nonnative hybrids have arisen spontaneously in the wild, while the remainder were introduced as hybrids.…”

DNA barcoding BritishEuphrasiareveals deeply divergent polyploids but lack of species-level resolution

“…In these cases, dispersal of haplotypes has clearly occurred and their sharing among species may be due to hybridisation and incomplete lineage sorting. The large number of reported hybrids and hybrid species based on morphology (Preston and Pearman, 2015, Stace et al, 2015), as well as the prevalence of hybridisation in genetic data (Stone, 2013, Liebst, 2008), point to hybridisation being a key factor shaping genetic diversity in Euphrasia . Future genomic surveys will estimate the proportion of loci introgressing across species barrier in models that explicitly account for incomplete lineage sorting (Twyford and Ennos, 2012).…”

An agenda for the future of biological recording for ecological monitoring and citizen science

“…A future priority is to extend existing projects and design new ones to collect information on environmental information associated with sightings. Options include: habitat information, associated species (Stewart et al ., ), behaviour, routes of invasion, hybridization (Preston & Pearman, ), conservation need, life history, etc. Comparative trait‐based studies that link trends with species’ traits has helped determine the mechanisms driving biodiversity loss (Fuller et al ., ; Powney et al ., ; Thomas et al ., ) and richer sighting data can increase the utility of species occurrence information to inform a range of ecological questions.…”