Abstract

In Dalechampia blossoms, anther-stigma distance (ASD) can influence self-pollination rates; blossoms with small anther-stigma distance values will experience more self-pollination. Self-pollination will cause the exposure of deleterious alleles then natural selection will purge from the popualtion. Additionally, when the small ASD can result in more pollen on the stigmas, it may increase pollen competition and thereby reduce inbreeding depression in offspring as more superior pollen will achieve fertilisation, The ASD (herkogamy) is thought to indicate a population’s mating history, and, if habitual inbreeders purge their genetic load, then the ASD should influence levels of inbreeding depression. This project aimed to assess if two self-compatible species, Dalechampia heteromorpha and D. scandens, displayed inbreeding depression and the level to which pollen competition could reduce its negative effects. In these species, hand-pollination experiments were performed controlling the amount of pollen load and the source of pollen (self vs. outcross). In D. scandens, four populations were classified as ‘predominant selfer’ (smallest ASD), ‘selfer’ (small ASD) and as ‘outcrosser’ (large ASD). The populations received hand-pollination experiments with the amount of pollen load varied. It was hypothesised that the ‘predominant selfer’ and ‘selfer’ populations have experienced a long inbred history whereas ‘outcrosser’ populations require pollinator services. The results from D. heteromorpha and D. scandens revealed that the offspring suffered from outbreeding depression at the early traits (pre-germination); in D. heteromorpha, inbreeding depression was detected in the later traits (post-germination). Increased pollen competition (higher pollen loads) increased the early fitness traits; especially for cross-pollination treatment, however, in the later traits saw a decrease in fitness. It was hypothesis that stigma blocking occurred, reducing the chance of superior pollination. Overall, pollen competition performed weaker than expected, it is likely to be occurring but it is mild and difficult to detect. The floral morphology for D. heteromorpha and D. scandens displayed a reduced ASD suggesting they are inbred. These findings agree that inbred species exhibit less inbreeding depression. The results from the comparison of the D. scandens populations show; that seed weight was lower in the ‘predominant selfer’ and ‘selfer’ populations. In addition, germination rate was lowest in the ‘predominant selfer’, but highest in the ‘selfer’ and the ‘outcrosser’ populations fell in between the two. Increased pollen competition improved fitness in the ‘predominant self’ yet it was not detected in the other populations. The lack of strong positive effects from pollen competition in the ‘outcrosser’ populations, could suggest that, if floral morphology affects self-pollination rates, a certain level of inbreeding may be beneficial for the offspring. In addition, this study detected that there was a positional affect in D. scandens; the central pistil frequently produced greater numbers of seeds, heavier seeds and increased chance of germination, regardless of treatment. Further to this, it was also found that two simultaneous pollinated blossoms on different branches were not independent. When two blossoms were pollinated with the same pollen origin there was an increased likelihood of abortion, suggesting that D. scandens can detect and favour increased genetic diversity of the offspring between blossoms. 

Additional Notes

Supervisors: Scott Armbruster and Rocío Pérez-Barrales

Course: Master of Philosophy - MPhil

Date Deposited: 2017-05-17

URI/permalink: https://library.port.ac.uk/dissert/dis12889.html