ST. KILDA SOAY SHEEP & MOUSE PROJECTS: ANNUAL REPORT 2009 J.G. Pilkington 1, S.D. Albon 2, A. Bento 4, D. Beraldi 1, T. Black 1, E. Brown 6, D. Childs 6, T.H. Clutton-Brock 3, T. Coulson 4, M.J. Crawley 4, T. Ezard 4, P. Feulner 6, A. Graham 10 , J. Gratten 6, A. Hayward 1, S. Johnston 6, P. Korsten 1, L. Kruuk 1, A.F. McRae 9, B. Morgan 7, M. Morrissey 1, S. Morrissey 1, F. Pelletier 4, J.M. Pemberton 1, 6 6 8 9 10 1 M.R. Robinson , J. Slate , I.R. Stevenson , P. M. Visscher , K. Watt , A. Wilson , K. Wilson 5. 1Institute of Evolutionary Biology, University of Edinburgh. 2Macaulay Institute, Aberdeen. 3Department of Zoology, University of Cambridge. 4Department of Biological Sciences, Imperial College. 5Department of Biological Sciences, Lancaster University. 6 Department of Animal and Plant Sciences, University of Sheffield. 7 Institute of Maths and Statistics, University of Kent at Canterbury. 8Sunadal Data Solutions, Edinburgh. 9Queensland Institute of Medical Research, Australia. 10 Institute of Immunity and Infection research, University of Edinburgh POPULATION OVERVIEW ..................................................................................................................................... 1 REPORTS ON COMPONENT STUDIES .................................................................................................................... 4 Vegetation ..................................................................................................................................................... 4 Weather during population crashes .............................................................................................................. 6 Sexual conflict in Soay twins......................................................................................................................... 7 Maternal effects and early-life performance are associated with parasite resistance across life................. 9 Autoimmunity in Soay sheep on St Kilda..................................................................................................... 12 A pilot study to find genes contributing to variation in Soay sheep body size……………………………....... 14 Soay sheep and admixture........................................................................................................................... 15 Mapping the Horns gene in Soay sheep ...................................................................................................... 17 Identifying parasite resistance genes in Soay sheep and in other breeds.................................................... 19 Ecology and evolution of the St Kilda field mouse...................................................................................... 21 PUBLICATIONS . ................................................................................................................................................. 23 ACKNOWLEDGEMENTS .. ................................................................................................................................... 24 APPENDIX A: PERSONNEL CHANGES & SCHEDULE OF WORK ........................................................................... 25 CIRCULATION LIST ........................................................................................................................................... 26 The sheep population on Hirta entered 2009 at a hig level of mortality than normal in a non-crash year. area between March and May of 2009. Lambing began o surviving (Fig. 1). 20 18 16 P 14 OPULATION 12 Lambs born10 8 6 4 2 O VE R V I E W 0 Figure 1. 20/03/ 2009 100 htagged level and,sheep as were a result, found there dead was within a slightly the study high 22/03/2009 In December 2009, 748 tagged24/03/200 sheep9 were believed to study area, a total increase of 11%26/03 using/2009 the study The temporal distribution of lamb births during 20 n the 20th of March with 78% of lambs born the population is shown in Fig. 2 and changes28/03/2009 in sh Fig. 3. 30/03/2009 01/04/2009 03/04/2009 100 05/04/2009 07/04/2009 90 09/04/2009 80 11/04/ 2009 70 13/04/2009 Date 15/04/2009 60 17/04/2009 50 Numbers 19/04/2009 40 21/04/2009 30 23/04/2009 er 25/04/2009 20 27/04/2009 10 29/04/2009 area since be alive the onprevious Hirta, ofyear. which The 617 age regularlydistribution used the 0 09. 01/ 05/2009 eep numbers in the study area over time0 3/are05/ 20 shown09 i Figure 2. 0(BW) 1(BR) 2(BO) 3(BY) 4(AG) 5(AL) 6(AW) 7(AR) 8(AO) 9(AY) 1 Age distribution of tagged Soay sheep presumed to Age (cohort tag) Males/females 0(YG) 11(YL) 12(YW) 13(YR) 14(YB) ?(OP) of n be alive at the end of 2009. 2 800 700 600 500 400 Sheep 300 200 100 0 5 9 3 9 3 7 8 8 9 9 0 0 9 9 9 9 0 0 1 1987 1 1991 1 1995 1997 1 2001 2 2005 2 2009 Year Figure 3. The number of tagged sheep regularly using the study area since 1985. One whole-island count yielded 2208 tagged and untagged sheep, with the details displayed in Table 1. The total population had increased by 15.6% since summer 2008, when it was at 1909. This gives a delta (calculated as ln (N t+1 /N t)) of 0.146 . Table 1. Demographic and geographic distribution of sheep observed during the count of Hirta on August 17 th 2009. Coat colours are DW = dark wild, DS = dark self, LW = light wild, and LS = light self. Location Females Males Lambs Total DW DS LW LS DW DS LW LS Conachair/Oiseval 179 5 72 1 74 1 25 0 191 548 Mullach Bi/Cambir 289 13 97 4 155 7 28 1 300 894 Ruaival/Village 257 11 99 3 94 1 24 0 277 766 Total 725 29 268 8 323 9 77 1 768 2208 3 REPORTS ON COMPONENT STUDIES Vegetation. Mick Crawley. The season of 2008-09 will be remembered as the-crash-that-never-happened. Very high sheep numbers in August 2008 combined with extremely low food availability in summer 2008 led us to think that the population was heading into the winter of 2008-09 in dire condition. Not only did the population fail to crash but, following a successful lambing in spring 2009, numbers increased to produce the highest total island count we have ever seen (there were 2208 animals in August 2009). The population appears to have been rescued from its anticipated fate by unusually high grass productivity through the autumn and winter of 2008, followed by above-average grass growth in spring and summer 2009. On the bright side, these results emphasize how important plant productivity can be as an explanatory variable for sheep population dynamics. A really important, but still unanswered question, is why the whole island sheep population is steadily increasing in size, year on year (Fig. 4). For the current study (post 1985) the average increase in population is more than 36 extra animals per year (p < 0.001). For the initial study (1954-68) the annual increase was roughly the same, at more than 34 animals per year, but for this shorter time-series, the trend falls short of significance (p = 0.095). Combining the data from the two studies produces a highly significant (p < 0.00025), but intriguingly shallower trend (with just under 13 extra animals per year; the dotted line in Fig. 4). We need to know what is driving this trend. It is plausible that plant productivity is increasing over time with climate change, and/or that the sheep are eating more of the vegetation biomass, or converting the plant biomass they eat into animal numbers more efficiently. Figure 4. Time series in sheep numbers (solid symbols) during the first study period (1954-68) and the current study period (1985-2009), showing the trends in population size within the two periods (solid regression lines) and averaged across the two study periods (dashed line; see text for details). No matter how we measure the trend, it is clear that the whole island population is increasing as the years go by. 4 One way of getting a handle on this is to look for matching long-term trends in the vegetation data. It is plausible that the upward trend in sheep numbers is associated with long-term declines in one or more components of the vegetation. It turns out that there has been a highly significant decline in August mean tussock mass in the inbye grasslands since 1994 (when this data series starts; p = 0.0002; Fig. 5). There as been no significant trend in mean gap mass over the same period (negative slope, but p = 0.29). It is no surprise that the biomass of tussocks is more responsive to fluctuations in sheep numbers than is the biomass of the perennially closely-cropped, lawn-like gaps. The trend in individual tussock mass correlates closely with a significant (p = 0.00047) long term negative trend in total August biomass (where tussock and gap mass are weighted by the proportional cover of gaps and tussocks). Similar patterns were observed in March biomass, but with a rather less significant decline in tussock total mass (p = 0.043) and, again, no decline in gap mass (p = 0.08). Figure 5. Average total dry plant mass (per 0.04m 2) in August for the grasslands inside the Head Dyke (inbye) in tussocks (upper solid line) and gaps (lower dotted line). There is a significant decline over time in the biomass of tussocks (p < 0.001) but no significant trend in the biomass of gaps (p = 0.29). Note that both tussocks (solid line) and gaps (dotted line) were relatively high in August 2009 (the right- hand ends of the two time-series point upwards) despite record high sheep numbers, reflecting the high grass productivity despite high offtake in the preceding months. As you can see (Fig. 5) the August 2009 biomass data from both gaps and tussocks buck the long-term downward trend, and these