Studies On Female Ornaments Of Threespine Stickleback (Gasterosteus Aculeatus)

In comparison with the extensive literature on male ornaments,little attention has been placed on female ornaments in animal kingdom until recently.Male ornaments are generally suggested to result from sexual selection while the explanations for the presence and evolution of female ornaments are categorized as either adaptive or non-adaptive.The adaptive explanation states that female ornaments arise from either female-female competition or male-mate selection on females while the non-adaptive explantion claims that female ornaments are due to the genetic correlation between the sexes in expression of the trait,combined with sexual selection on the male trait.According to Zahavi's handicap theory,extravagant ornaments are costly handicaps and only those individuals with high quality could afford them.Correlations between female ornaments and female quality or components of fitness may shed light on omaments' potential role as signals of individual quality.A positive correlation between female ormaments and female quality may support the adaptive explanations while no correlation or negative correlation suggests the non-adaptive explanation.Three correlated individual studies were carried out to explore the adaptive significance of female ornaments.The first study aimed at exploring whether female ornaments are correlated with phenotypic traits/fitness-related traits.The second study aimed at testing whether resource allocation to ornaments is associated with the allocation to reproduction.The third study aimed at checking the direct maternal effects on offspring survial and growth.In the first study,I chose two stream-resident populations of threespine stickleback(Gasterosteus aculeatus)(Little Campbell River,British Columbia and Matadero Creek,California),in which females often exhibit male?typical red throat coloration,and an anadromous population that lacks such coloration(also inhabits the Little Campbell River)as studying materials.By measuring body size(standard length),body mass,age,throat and spine coloration(see chapter 2 for detailed methods)for hundreds of fish captured from 2010 to 2012,1 tested whether red throat coloration in females was associated with the quality/fitness-related traits such as body condition(body mass/standard length?3),body size,age,and growth,and with red pelvic spine coloration.The major findings are shown as below.(1)Throat red intensity was positively correlated with body size in both stream-resident populations.And analysis about stream-resident females of Little Campbell suggested the reddest females grew fastest;older individuals also showed more intense throat coloration.(2)Throat red intensity was not correlated with body condition(body mass/standard length?3).(3)Red spine coloration was positively correlated with both throat color and body size within stream populations under most circumstances.Based on these results,it can be concluded that ornaments of the study populations could be an honest indictor for individual quality and could provide conspecific male with some important information.In the second study,I examined allocations of carotenoid to throat skin and eggs of female threespine stickleback.The conspicuous throat and spine color of threespine stickleback are due to the presence of carotenoid.Besides acting as the signal pigment,carotenoid also performs important physiological functions such as immune defence,anti-oxidation and protection in the early stage of embryonic development.According to the trade-off theory in evolutionary ecology,development of ornamented traits costs carotenoid that could have been used elsewhere.Therefore,the allocation of carotenoid between throat skin and other tissue(e.g.,eggs)may show a compromise.However,plentiful carotenoid supply may also result in a positive correlation of carotenoid in throat skin and in eggs.HPLC(high performance liquid chromatography)was used to qualify and quantify carotenoid in throat skin and eggs of female threespine sticklebacks(Gasterosteus aculeatus)captured from the Little Campbell River in British Columbia,Canada.Reflectance measurement and digital pictures analysis were used to calculate chroma(a measurement of redness)of throat skin and pelvic spines respectively.The major results are as follows.(1)Spine chroma was a good indicator of eggs total carotenoid concentration and higher spine chroma indicated higher eggs total carotenoid concentration in both 2010 and 2012.Meanwhile,higher throat chorma indicated higher eggs total carotenoid concentration in 2010 but indicated lower eggs total carotenoid concentration in 2012(spine color:F1,62=26.2369,P<0.0001;throat color:F1,60=4.2818,p=0.0428;year:F1,60=18.0812,p<0.001;interaction:F1,60=6.2753,p=0.0150).(2)There was a positive correlation between carotenoid concentration in throat skin and in eggs,no matter analyzing only total carotenoid or each single group separately(astaxanthin group or lutein group).Although annual variation exists,the positive correlation remained unchanged.The situation was similar when replacing concentration with absolute contents of carotenoid to represent the abundance.(3)Throat ehroma was not a reliable indicator of total earotenoid eoncentration in throat skin but could reliably indicate the astaxanthin proportion of total carotenoid concentration.In view of the positive correlation between carotenoid concentration in throat skin and eggs,trade-off of carotenoid allocation seems not exist between these two tissues.Pelvic spine color could well indicate eggs total carotenoid concentration while throat eolor could not.This may suggest two traits transmit information with more details in a combined manner.In the study,I observed an interesting phenomenon.When using acetone to extract carotenoid,the spine color disappeared instantly and the acetone immediately showed obvious orange or red color.But for throat skin,it usually took 48 hours to thoroughly extract carotenoid.The difference of time spent in acetone extraction may suggest the run off rate of carotenoid in spine is much higher than in throat skin.Spine color may convey the information about individual's instant carotenoid reserve while throat color may convey the information about individual's long-term carotenoid reserve.In the third study,to examine carotenoid's effects on fry development in the early stage of life history,I created half-sibs by artificially fertilizing eggs from two females who that are similar in standard length,body mass but di?herent in throat redness(indeed redder females showed higher eggs carotenoid concentration in the later HPLC test)with sperm from the same male.I monitored fiy and measured their standard length and body mass for 5 months.After analyzing collected data,following results were found.(1)The eggs spawned by red mothers are not different from the eggs spawned by dull mothers on size(eggs from redder mother VS.eggs from dull mother:3.74±0.09mg VS.3.68±0.09mg,p=0.648).(2)The eggs from red mother were more likely to be fertilized successfully in general(eggs from redder mother VS.eggs from dull mother:79.3±1.4%VS.66.4± 1.4%,p<0.001).(3)Offspring of red mother had obvious advantage on both standard length and body mass over offspring of dull mother.(4)Offspring from red and dull mother were not significantly different in mortality in the first 150 days of life history.Based on these results,I suggest that higher carotenoid concentration in eggs could give fry some advantage on growth.However,I cannot exclude the possibility that fiy hatched from eggs with lower carotenoid concentration may have advantage on other aspects such as immune defence considering an existing study(Barber et al.,2001).To summarize,in view of the results of above individual studies,I believe that the female ormaments of threespine stickleback in Little Campbell River,BC,Canada could indicate individual quality such as standard length,growth rate and even carotenoid concentration in the eggs.Based on the information provided by ormaments,males of the same population could evaluate reproductive payoff.Indeed,fry hatched from the eggs with higher carotenoid concentration have some advantages on growth and development.Therefore,the female ornaments based on carotenoid in threespine stickleback seem to be honest signals to show their potentials on growth and reproduction.