Differences in flowering phenology, architecture, sexual expression and resource allocation between a heavily haired and a lightly haired nettle population: relationships with sika deer

Intense Browsing by Sika Deer (Cervus Nippon) Drives the Genectic Differentiation of Hairy Nettle (Urtica Thunbergiana) Populations

“…Several studies demonstrated that a single herbivore species causes plant species to evolve resistant traits (e.g., the relationship between diamond-back moth Plutella xylostella and perennial herb Arabidopsis lyata; see Introduction) but no studies revealed that the herbivore even leads genetic differentiation among plant populations. Nettles under intense browsing by sika deer exhibit not only heavy hairiness but also low plant height, high degree of branching, early and long owering, high resource allocation to leaves and in orescences, and dominance of monoecy compared with those almost free from deer browsing (Hirata et al 2019). These characteristics would help to enhance resistance and tolerance to sika deer and to reduce damages on growth and reproduction (Hirata et al 2019).…”

“…Nettles under intense browsing by sika deer exhibit not only heavy hairiness but also low plant height, high degree of branching, early and long owering, high resource allocation to leaves and in orescences, and dominance of monoecy compared with those almost free from deer browsing (Hirata et al 2019). These characteristics would help to enhance resistance and tolerance to sika deer and to reduce damages on growth and reproduction (Hirata et al 2019). The expression of these traits should be under the control of many genes, most of which may be located on the outlier loci assigned in this study.…”

“…As mentioned above, TO is subjected to intense deer browsing. This should exert a strong selective pressure on this population to maintain not only heavy hairiness but also small stature, high degree of branching, early and long owering period, high resource allocation to leaves and owers, and dominance of monoecy (Hirata et al 2019). These characteristics would help to enhance resistance and tolerance to sika deer and to reduce damages on growth and reproduction (Hirata et al 2019).…”

“…In NP, several hundred sika deer (Cervus nippon (Artiodactyla, Cervidae) have been protected for more than 1,200 years as sacred animal. Our previous work has revealed that heavily-haired nettles in NP are resistant to sika deer but not herbivorous insects such as the red admiral Vanessa indica (Kato et al 2008;Iwamoto et al 2014) and that variation in hairiness among nettle populations are genetically based (Kato et al 2008;Hirata et al 2019). These ndings suggest that heavy hairiness has evolved through natural selection under intense browsing by sika deer.…”

Herbivory enhances leaky sex expression in the dioecious herbMercurialis annua

“…By reducing plant size and resource availability, herbivory in dioecious populations may directly increase mortality of individuals with the more costly sex function, potentially leading to or enhancing sex ratio biases (Cornelissen and Stiling 2005, Geber et al 2012. For similar reasons, herbivory in hermaphroditic species can cause individuals to shift their investment towards the least costly sexual function (Diggle 1994, Seger and Eckhart 1996, Ashman 2002, Zhang and Jiang 2002, West 2009, Hirata et al 2019. A particularly interesting and important possibility is that herbivory could influence the sex allocation of males and females of dioecious species by altering their tendency to produce flowers of the opposite sex through 'leaky' or 'inconstant' sex expression.…”