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The monoculture effect: A meta-analysis and experiment on ostrich chicks

Bensch, Hanna (2017) BIOP01 20162
Degree Projects in Biology
Abstract
The spread of pathogens between individuals has important effects on patterns of mortality, behaviour and the genetic structure of populations. One factor that is predicted to influence the transmission of pathogens is the genetic diversity of the host group. Groups of closely related individuals are susceptible to similar pathogens, and hence increase in genetic diversity of the group should decrease pathogen transmission between hosts. This has popularly been referred to as the ‘monoculture effect’ as a result of the increased risk of disease in agricultural crop monocultures. However, empirical studies have found evidence both for and against the monoculture effect, raising the question of whether it is simply an artefact of agriculture... (More)
The spread of pathogens between individuals has important effects on patterns of mortality, behaviour and the genetic structure of populations. One factor that is predicted to influence the transmission of pathogens is the genetic diversity of the host group. Groups of closely related individuals are susceptible to similar pathogens, and hence increase in genetic diversity of the group should decrease pathogen transmission between hosts. This has popularly been referred to as the ‘monoculture effect’ as a result of the increased risk of disease in agricultural crop monocultures. However, empirical studies have found evidence both for and against the monoculture effect, raising the question of whether it is simply an artefact of agriculture and therefore not applicable to natural populations. In this study, I investigate the strength and generality of the monoculture effect in a range of species, by conducting a meta-analysis of the relationship between within group genetic diversity and pathogen prevalence and/or mortality. In total, I found 33 relevant studies (on 20 species), and the meta-analysis showed a significant negative relationship between group genetic diversity and rates of host infection/mortality, confirming that the monoculture effect is a general phenomenon. One issue with the study of the monoculture effect highlighted by this analysis was that the majority of the studies were on insects and that more research is required on a broader range of taxa. I addressed this issue by conducting a study on juvenile ostriches, Struthio camelus, where I experimentally manipulated the genetic diversity of clutches and examined the effect on chick growth and survival. In contrast to the predicted monoculture effect, I found that group genetic diversity was not related to survival and that chicks from groups with low genetic diversity grew larger than chicks from groups of high genetic diversity. This potentially indicates that kin-selection, which favours beneficial interactions between relatives, may counter-act the detrimental effects of low genetic diversity within groups. Survival varies widely between years and was unusually high during this experiment (less than 6 % died from disease) indicating that the balance between the monoculture effect and benefits gained by kin selection may be context-dependent. (Less)
Popular Abstract
Benefit of living with strangers?

Nowadays, crops are normally grown in big monocultures, with only one variety of the plant in the same field and no other species mixed with them. This has shown to make fields more vulnerable to infection from pathogens and parasites resulting in potential severe losses in yield. Increasing the number of varieties of the plant in fields has been showed to decrease the spread of pathogens within the fields and increase yields: there is a benefit of lower relatedness and higher diversity within populations to increased disease resistance. This phenomenon is called the ‘Monoculture effect’.

But is the monoculture effect only a phenomenon among dense plant populations? Or is high genetic diversity and... (More)
Benefit of living with strangers?

Nowadays, crops are normally grown in big monocultures, with only one variety of the plant in the same field and no other species mixed with them. This has shown to make fields more vulnerable to infection from pathogens and parasites resulting in potential severe losses in yield. Increasing the number of varieties of the plant in fields has been showed to decrease the spread of pathogens within the fields and increase yields: there is a benefit of lower relatedness and higher diversity within populations to increased disease resistance. This phenomenon is called the ‘Monoculture effect’.

But is the monoculture effect only a phenomenon among dense plant populations? Or is high genetic diversity and low relatedness within groups also beneficial for decreasing pathogens within populations of other organisms? I conducted a meta-analysis, a systematic review of published articles to investigate this question further. My results showed that benefits of low relatedness and high genetic diversity within groups could be found within many different classes organisms and studies. Dense plant populations were found having the strongest effect of monoculture effect, but were far from the only species benefiting of lower relatedness within groups.

The meta-analysis included a majority of articles studying insects and only a few studies on larger animals. For the second part of my thesis did I therefore conduct an experiment on within group relatedness effect on ostrich chick survival and growth. Ostrich chicks can experience high variation in growth rate and survival between years, and clutches of chicks can vary in within relatedness as adult ostriches are promiscuous. This makes ostrich chicks optimal to test the monoculture effect on, as clutches in the wild in theory should vary in within clutch relatedness.

My experiment followed survival and growth of 120 ostrich chicks during their first eight weeks at an experimental farm in South Africa. Chicks were put into 15 groups, ranging from higher to lower within group relatedness. After eight weeks had total of 14 chicks died, and I found no effect of within group relatedness to group survival, rejecting the monoculture effect as a phenomenon within this study. Chicks from groups of high relatedness actually grew bigger than chicks of groups of low relatedness in contrast to what expected by the monoculture effect. But maybe under harsher years, when pressure from pathogens are stronger, will there be an effect of the monoculture effect to the chicks’ survival and growth. Then maybe cooperation among closely related chicks is not as beneficial as living in groups where pathogen transmission is lowered due to lower relatedness.


Master’s Degree Project in Biology 60 credits 2017
Department of Biology, Lund University

Advisor: Charlie Cornwallis
Molecular Ecology and Evolution Lab (Less)
Please use this url to cite or link to this publication:
author
Bensch, Hanna
supervisor
organization
course
BIOP01 20162
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8906242
date added to LUP
2017-04-27 11:36:58
date last changed
2017-04-27 11:36:58
@misc{8906242,
  abstract     = {The spread of pathogens between individuals has important effects on patterns of mortality, behaviour and the genetic structure of populations. One factor that is predicted to influence the transmission of pathogens is the genetic diversity of the host group. Groups of closely related individuals are susceptible to similar pathogens, and hence increase in genetic diversity of the group should decrease pathogen transmission between hosts. This has popularly been referred to as the ‘monoculture effect’ as a result of the increased risk of disease in agricultural crop monocultures. However, empirical studies have found evidence both for and against the monoculture effect, raising the question of whether it is simply an artefact of agriculture and therefore not applicable to natural populations. In this study, I investigate the strength and generality of the monoculture effect in a range of species, by conducting a meta-analysis of the relationship between within group genetic diversity and pathogen prevalence and/or mortality. In total, I found 33 relevant studies (on 20 species), and the meta-analysis showed a significant negative relationship between group genetic diversity and rates of host infection/mortality, confirming that the monoculture effect is a general phenomenon. One issue with the study of the monoculture effect highlighted by this analysis was that the majority of the studies were on insects and that more research is required on a broader range of taxa. I addressed this issue by conducting a study on juvenile ostriches, Struthio camelus, where I experimentally manipulated the genetic diversity of clutches and examined the effect on chick growth and survival. In contrast to the predicted monoculture effect, I found that group genetic diversity was not related to survival and that chicks from groups with low genetic diversity grew larger than chicks from groups of high genetic diversity. This potentially indicates that kin-selection, which favours beneficial interactions between relatives, may counter-act the detrimental effects of low genetic diversity within groups. Survival varies widely between years and was unusually high during this experiment (less than 6 % died from disease) indicating that the balance between the monoculture effect and benefits gained by kin selection may be context-dependent.},
  author       = {Bensch, Hanna},
  language     = {eng},
  note         = {Student Paper},
  title        = {The monoculture effect: A meta-analysis and experiment on ostrich chicks},
  year         = {2017},
}