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Congratulations to Erin Cullen on her publication in the Annals of Botany

last modified Feb 06, 2018 08:50 AM

Congratulations to Erin Cullen, 2015 cohort PhD student in the BBSRC DTP Programme, for publishing the paper Evolution of nectar spur length in a clade of Linaria reflects changes in cell division rather than in cell expansion in Annals of Botany.



Background and Aims

Nectar spurs (tubular outgrowths of a floral organ which contain, or give the appearance of containing, nectar) are hypothesized to be a ‘key innovation’ which can lead to rapid speciation within a lineage, because they are involved in pollinator specificity. Despite the ecological importance of nectar spurs, relatively little is known about their development. We used a comparative approach to investigate variation in nectar spur length in a clade of eight Iberian toadflaxes.


Spur growth was measured at the macroscopic level over time in all eight species, and growth rate and growth duration compared. Evolution of growth rate was reconstructed across the phylogeny. Within the clade we then focused on Linaria becerrae and Linaria clementei, a pair of sister species which have extremely long and short spurs, respectively. Characterization at a micromorphological level was performed across a range of key developmental stages to determine whether the difference in spur length is due to differential cell expansion or cell division.

Key Results

We detected a significant difference in the evolved growth rates, while developmental timing of both the initiation and the end of spur growth remained similar. Cell number is three times higher in the long spurred L. becerrae compared with L. clementei, whereas cell length is only 1.3 times greater. In addition, overall anisotropy of mature cells is not significantly different between the two species.


We found that changes in cell number and therefore in cell division largely explain evolution of spur length. This contrasts with previous studies in Aquilegia which have found that variation in nectar spur length is due to directed cell expansion (anisotropy) over variable time frames. Our study adds to knowledge about nectar spur development in a comparative context and indicates that different systems may have evolved nectar spurs using disparate mechanisms.

Read the full paper.


Erin is researching the evolution and development of floral traits influencing pollinator behaviour in the lab of Professor Beverley Glover in the Department of Plant Sciences. As part of the BBSRC DTP Programme she completed rotation projects with Professor Glover and with Professor Howard Griffiths, also in Plant Sciences. Erin is currently undertaking a RCUK internship with the Parliamentary Office of Science and Technology (POST).