Copepod sex ratio dynamics: the role of predators and food
Lead Research Organisation:
Queen Mary University of London
Department Name: Sch of Biological and Chemical Sciences
Abstract
Copepods are free-drifting animal plankton found throughout the ocean in vast numbers. This group plays a critical role in the biochemistry of the upper ocean. They are the dominant grazers of many phytoplankton (free floating plants) and central to the food web, being the food source of many larger predators including some commercial fish. Through their actions they move carbon from surface waters to the deep ocean (the biological pump). In order to quantify and model the biogechemistry of the upper ocean, the mechanisms involved in determining copepod population size need to be understood. Changes in population abundance are determined by fecundity, growth and mortality rates. Whilst there is a strong understanding of copepod growth and fecundity, few field studies on mortality have been undertaken, and a mere handful have attempted to identify the causes of death. Consequently there are fundamental gaps in our understanding of controls on population dynamics in this important planktonic group. In many species the ratio of males and females at the birth is close to 1 (i.e. equal numbers of each) and evolutionary and genetic arguments suggest the same should be true for copepods. However, other factors can then act to alter this intial ratio as the animals age, for example, the males may die faster. Whilst in some copepod species there are equal numbers of the sexes in adults, in others the ratio is highly skewed (with females outnumber males by 10 to 1 or more). Evidence suggests that production of young by adult copepods can be limited by mate encounters, these are controlled by the sex ratio. Sex ratios are therefore both critical in population growth, and they also can give us an insight into the causes of mortality. The adult sex ratio is the result of events in this stage and/or earlier juveniles. Our first objective is therefore to quantify where sex ratio skew is generated. We will do this for populations of 3 chosen copepod species at a site in Southampton Water (UK) over an annual cycle. The copepod species being Acartia discaudata, Pseudocalanus elongatus and Oithona nana. Next, the two likely contributors to adult sex ratio skew will be studied, these are: 1. Differences in feeding rates on males and females by predators In searching for mates the behaviour of males increases the likelihood of their detection and predation. Predation rates on the 3 copepods will be determined in laboratory feeding experiments with 2 pelagic predators (the scyphomedusa Aurelia aurita and the chaetognath Sagitta setosa) over a range of adult copepod prey densities, and male to female ratios. Sex-specific differences in predation rates on marine copepods will be tested. 2. Differences in males and female physiological longevity Many males live for shorter periods than females when they are incubated free from any predators, they have a shorter 'physiological' longevity. This can be related to the fact that many males feed at reduced rates. Males and females of the 3 chosen copepods will be examined across a range of food concentrations and compositions in the laboratory to quantify these differences. At the Southampton Water site the chosen prey and predators co-occur. Over an annual cycle we will estimate mortality rates of the 3 copepods and also perform gut content analysis of the 2 predators to examine their removal rates. By combining field mortality rates, physiological longevity ranges and predator rates on the copepods we will produce a mortality budget. Our work has important implications beyond the local study site. A mathematical model that combines the adult age-survival functions with external (predation) mortality to determining sex ratios will be developed. Combined with global field sex ratios, we will make predictions of the relative control of food and predators. An optimal life-history model will be developed in order for us to examine differences between copepod sexes and families.
People |
ORCID iD |
Andrew Hirst (Principal Investigator) |
Publications
De Paula WB
(2013)
Female and male gamete mitochondria are distinct and complementary in transcription, structure, and genome function.
in Genome biology and evolution
De Paula WB
(2013)
Energy, ageing, fidelity and sex: oocyte mitochondrial DNA as a protected genetic template.
in Philosophical transactions of the Royal Society of London. Series B, Biological sciences
Fitzgeorge-Balfour T
(2014)
Influence of copepod size and behaviour on vulnerability to predation by the scyphomedusa Aurelia aurita
in Journal of Plankton Research
FitzGeorge-Balfour T
(2012)
Estimating digestion time in gelatinous predators: a methodological comparison with the scyphomedusa Aurelia aurita
in Marine Biology
Hirst A
(2013)
Female-biased sex ratios in marine pelagic copepods: Comment on Gusmão et al. (2013)
in Marine Ecology Progress Series
Hirst A
(2010)
Does predation controls adult sex ratios and longevities in marine pelagic copepods?
in Limnology and Oceanography
Venton D
(2013)
Highlight: on the origin of the sexes.
in Genome biology and evolution
Description | We have published a range of papers to date from this funded research. These have increased understanding of how the jellyfish Aurelia aurita (moon jellyfish) selects prey on the basis of size, sex and mobility of prey. This has also included an examination of digestion times in this predator, important when determining selection in the field from analysing the contents of animals stomachs, a common field method for the field. We have also developed understanding of controls on the ratio of adult male to female numbers in copepods. |
Exploitation Route | Our research publications will help others in defining sex selective predation in pelagic predators, and the role this plays in determining sex ratio and their skew in copepods. Copepods are a critical step in marine and freshwater pelagic food webs, and are the most numerous animals on the planet. |
Sectors | Education,Environment |
URL | http://horne1991.wix.com/thehirstlab#!news/c1rh8 |
Description | The work has been published, but also showcased at the Horniman museum to the public. It has also been presented at several academic conferences. Finally the work was written up in an edition of NERC News. |
First Year Of Impact | 2011 |
Sector | Education,Environment |
Impact Types | Societal |
Description | Collaboration with Horniman Museum Aquarium |
Organisation | Horniman Museum and Gardens |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | We provided the intellectual drive of the project. We performed the experiments, analysed the data and wrote the papers. We produced material with them in order to display this to the public at the Horniman Museum. |
Collaborator Contribution | The Horniman Museum aquarium provided us with jellyfish for predation experiments and a public outreach opportunity. We provided the aquarists with space on our field trips for collection. We co-published work together in two of our papers. We also used their public aquarium to reach a wide audience in presenting our work as poster display there. The aquarist provided advice on maintaining the jellyfish and in general husbandry. |
Impact | FitzGeorge-Balfour T, Hirst AG, Lucas CH, Craggs J (2013) Influence of copepod size and behaviour on vulnerability to predation by the scyphomedusa Aurelia aurita. Journal of Plankton Research 36: 77-90. doi: 10.1093/plankt/fbt077 FitzGeorge-Balfour T, Hirst AG*, Lucas CH, Craggs J, Whelan EJ, Mombrikotb S (2013) Estimating digestion time in gelatinous predators - a methodological comparison with the scyphomedusa Aurelia aurita. Marine Biology 160: 793-804 Presentation material at the Horniman Museum. |
Start Year | 2010 |
Description | The Jellyfish Banquet - examining differences in the suceptability of copepods to capture by Aurelia aurita. |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | Yes |
Geographic Reach | Regional |
Primary Audience | Schools |
Results and Impact | We have been collaborating with the aquarium at the Horniman museum, London and they have this poster describing our work on permanent display We did not solicit feedback, however, the museum and aquarium have huge audiences every day and our work was displayed prominently, as such we are aware we reached and educated a large number (many thousands) of children, young adults, and adults. |
Year(s) Of Engagement Activity | 2010 |