DOI: 10.5061/dryad.q83bk3jm2
title: Evidence of hybrid breakdown among invasive hybrid cattails (Typha x glauca)

description: Interspecific hybridization has varied consequences for offspring fitness,
 with implications for the maintenance of species integrity. Hybrid vigour,
 when it occurs, can peak in first-generation (F1) hybrids and then decline
 in advanced-generation (F2+) hybrids. This hybrid breakdown, together with
 the processes affecting patterns of hybridization and hybrid fitness,
 determine the evolutionary stability of hybrid zones. An extensive hybrid
 zone in North America involving the cattails Typha latifolia, T.
 angustifolia, and their invasive hybrid T. × glauca is characterized by
 hybrid vigour among F1s, but the fitness of advanced-generation hybrids
 has not been studied. We compared seed germination and plant growth of T.
 latifolia (parental L), F1 T. × glauca (F1), hybrid backcrosses to T.
 angustifolia (bcA) and T. latifolia (bcL), and advanced-generation (F2)
 hybrids. Consistent with expectations under hybrid breakdown, we found
 reduced plant growth for F2 hybrids in comparison with F1s (plant height
 and above-ground biomass) and parental Ls (above-ground biomass).
 Backcrossed hybrids had intermediate measures of plant growth and bcLs
 were characterized by reduced seed germination in comparison with parental
 Ls. Hybrid breakdown could make the formation of F1s in North America
 finite because (1) hybridization among cattails is asymmetric, with T.
 angustifolia but not T. latifolia subject to genetic swamping, and (2) T.
 angustifolia is less common and subject to competitive displacement by
 F1s. Hybrid breakdown is therefore expected to reduce hybrid frequencies
 over time, contributing to the long-term maintenance of T. latifolia – the
 only native cattail in the study region.
description: <strong>Data collection</strong>
 The data in the corresponding paper involved two phases: (1) hand
 crosses conducted in natural populations of cattails; (2) the germination
 and growth of seedlings arising from the hand crosses. Crosses were
 conducted with the aim of creating de novo F<sub>1</sub>
 hybrids (<em>T. latifolia x</em> <em>T.
 angustifolia</em>), F<sub>2</sub> hybrids
 (F<sub>1</sub> x F<sub>1</sub>), the two types of
 back-cross hybrids both with F<sub>1</sub>s as the maternal
 parent (backcross to <em>T. angustifolia,</em> bcA; backcross
 to <em>T. latifolia</em>, bcL). Seed set, germination and
 growth of these plants was compared to that of <em>T.</em>
 latifolia, also generated from hand crosses (<em>T.
 latifolia </em>x <em>T. latifolia</em>). Seed set was
 estimated using a subsample of the fruit. Germination was assessed in
 petrie dishes placed in a greenhouse. Seedlings were transplanted into
 pots and grown in the same greenhouse. After 90 days of growth plant
 height and above-ground biomass were measured for each seedling.
 <strong>Data processing</strong>
 Data processing and analysis were conducted using R and the
 scripts used are included alongside the data.
description: We used R to analyse the data, however, the files are in txt and
 csv format and can be opened using a variety of proprietary and
 open-source alternatives.