Abstract Detail

Reproductive Processes

Castro, Mariana [1], Husband, Brian [2], Loureiro, Joao [1], Castro, Sílvia [3].

The role of multiple reproductive barriers: Strong post-pollination interactions govern cytotype isolation in the tetraploid-octoploid Gladiolus communis contact zone.

Polyploidy is an important contributor to sympatric speciation and assortative mating is a key mechanism driving cytotype interactions at contact zones. While strong reproductive barriers can mediate the coexistence of different cytotypes in sympatry, positive frequency-dependent mating disadvantage ultimately drives the transition to single-ploidy populations. Still, comprehensive estimates of reproductive isolation among cytotypes and across multiple barriers are scarce. In this work we quantified the strength of isolation across multiple reproductive stages in a tetraploid-octoploid contact zone to understand the potential for coexistence. For that, assortative mating due to flowering asynchrony, pollinator behaviour, morphological overlap, self-fertilization and gametic competition between tetraploid and octoploid Gladiolus communis in a contact zone in Western Iberian Peninsula were assessed in natural and experimental populations to quantify reproductive isolation (RI) between cytotypes. Tetraploids and octoploids present a high degree of overlap in flowering time, similar floral morphology, and are visited by generalist insects without cytotype foraging preferences, resulting in weak pre-pollination reproductive isolation (RI from 0.00 to 0.21). In contrast, post-pollination isolation resulting from gametic selection was a strong barrier to inter-cytotype mating, with ploidy composition in stigmatic pollen loads determining the levels of RI (RI from 0.54 to 1.00). Also, between-cytotype cross-incompatibility was relatively high (RI from 0.54 to 0.63) as was isolation acquired through self-pollination (RI of 0.59 in tetraploids and 0.39 in octoploids). In conclusion, we show that total RI was high for both tetraploids (RI from 0.90 to 1.00) and octoploids (RI from 0.78 to 0.98). Such high rates of assortative mating will enable cytotype coexistence in mixed-ploidy populations by weakening the impacts of minority cytotype exclusion. With this presentation we will reveal the key role of gametic selection in cytotype siring success and highlight the importance of comprehensive estimates across multiple reproductive barriers to understand cytotype interactions at contact zones.

1 - University Of Coimbra, CFE-Centre For Functional Ecology, Department Of Life Sciences, Cal�ada Martim De Freitas, Calçada Martim De Freitas, Coimbra, 3000-456, Portugal
2 - University Of Guelph, Integrative Biology, 50 Stone Road E, Guelph, ON, N1G 2W1, Canada
3 - University Of Coimbra, CFE-Centre For Functional Ecology, Department Of Life Sciences, Calçada Martim De Freitas, Coimbra, 3000-456, Portugal

Keywords:
contact zone
cytotypes
gametic barriers
Gladiolus communis
phenology
pollen load composition
pollinator preference
polyploidy
unreduced gametes.

Presentation Type: Oral Paper
Session: REP3, Reproductive Processes 3
Location: Virtual/Virtual
Date: Thursday, July 30th, 2020
Time: 10:15 AM
Number: REP3002
Abstract ID:613
Candidate for Awards:None