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3C03 lecture 2.docx

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McMaster University
Life Sciences
Brett Beston

Psych Lecture 2---Sexual Selection and Mating systems Polygamous mating systems - either male or female have more than one mate during mating system - can include polygyny- males have more than one female at any one time - polyandry- females mate with more than one male - circles of male territory may encircle female territory - scramble polygyny—when it is not economical depending on resource of female or range of male is not possible- so male travels back and forth and maintain status of females – occurs when you have explosive reproductive cycle- e.g. female is only fertile in small windows or limited day, so male capitalize on small differences in females - resource defense polygyny- males tend to be holders of resources within their environment and thus females who are willing to enter in male’s territory will be receptive to that male - female defense- males provide defense to females - leks- female choice model- group of males together and female chose who she is willing to mate with Female defense polygyny - occurs when females are social animals and their movement is predictable - males can defend large group of females permanently or seasonally - Australian wasps – males will mature faster than females and when they mature, they search up for unopened cells and females tend to be clumped together, so males guard the unhatched females – benefit form this- as soon as virgin female emerges from egg or cocoon and the closest male present themselves and mate with female right away—male capitalize on small window of receptivity - Male is defending space he knows female is in—open himself up to polygynous mating systems Characteristics of polygyny - fecundity= reproductive life span Lek polygyny - lekking= arena mating - studied in birds and mammals, amphibians, fish and insects (classes of flies) - e.g. no paternal care in terms of parental care - males set up and defend small arenas ( temp. territories) – 4 or 5 males aggregate in arena and show case themselves and puffing display - males do not provide them with no resource for female to care for their young except sperms - leks benefit females in choice making decisions - males tend to have ornamentations , look different from females and sounds produced— male tend to aggregate within a single lek and several of them – and often a single male will obtain a greatest proportion of all females as they enter into a lek- sometimes more than 80%-- a lot of competition in leks - e.g. I 80% of males get all mating and n=10, so only 20% of mating with other males – competition high since a lot of males that will have no opportunity to reproduce - paradox of lek--- persistent female choice and they should erode level of genetic variance between males- e.g. only choosing one mate, should the sons of that mate not look similar , the differences should start to go away over time ( and inbreeding might start to occur- greater similarity among males) - despite above, every generation, female will select one male in vast majorities of mate competitions - 2 questions- what are the benefits females tend to receive from this mate choice and 2. What benefits are males getting from this - females get few direct benefits—so that means females must be selecting male mates based on indirect benefits Variance and polygyny - males benefit from sexiest male - variance tend to be spread of reproductive success that individual will receive over a lifetime - capture reproductive variance of all males—some males receive lower than average mating but few males will receive extraordinary reproductive success--- large spread/variance - female offspring, particularly sons--- may be more attractive Sexy son hypothesis - experiment--- establish lek where they put 10 males in an arena and allowed one female in at a time and made decision as to who she chose to mate with - went on until 10 females – each female allowed to choose individually - then took most attractive male and then left only unattractive males – so females could only chose from the unattractive portion - see how above affects outcome of offspring—compare sexy male v.s. un sexy male reproductive success Graph - benefits based on female choice - mean survival of sons and daughters and distinguish their survival based on previous female choice of father - result- systematic difference between males and females---- low attractive fathers survival offspring is not impacted in any way—mate choice does not just influence genes of offspring in some way- no evidence of good gene model since no difference in survival - some support for sexy son hypothesis --- e.g. placed offspring in lek—outcome- females showed strong mating preference for sons of attractive fathers - second graph- mean mating success of sons- advantage to sons of attractive fathers – evidence to suggest female mate choice decision is not based on good genes but rather to produce offspring that are attractive to next generation and more reproductive success for their son in the next generation Ecology and evolution of polygynous mating systems - when will female engage in polygymous or monogamous relationship - how do females make a choice on who to choose for a partner - resources tend to limit females in some way and what limits males is access to females - polygyny in context or resource dispersal and how this affect prob. That female will engage in polygynous relationship Should male have one or many mates? - tied to dispersion of sexes - females can often fertilize all of her eggs with single males but her reproductive success is not tied to availability of mates but resources - more resources available to female, the more she can reproduce - males can fertilize many eggs so their success is tied more to females - where females go depend on where resources are - how many mates males get depends on how much resources/size of territory male can guard Pattern of resource dispersal - random, regular or clumped - see how male benefit from this - random—depend on where they are located- if male can protect territory and how many male gets depend on how many random resources are in that environment - cluster- lots of resource-s- high male competition for territory and the benefits is that this gets more area than other territory - e.g. seal population- found aggregated in ice packs or land--- seals on ice packs are widely dispersed and males typically guard from single to few females - random distribution—in land or breaches—females socially aggregate areas of abundant resources- clustered organization and allow male seals that have up to 40 females present - male that defends larger space defends larger number of males - ecological—dispersal and size of resources male can hold - spacing of females affect what territories males will try to hold—most important determining factor - females should just care where resources are - both males and females go towards where resources are and only strongest males are defending area—possible hypothesis Ims - Ims: test hypothesis by affecting dispersal of males and females - Manipulate spacing and clustering- cage female voles and artificially manipulate their dispersal—some cases, female evenly distributed and sometimes have more than on female in single cage - Then track behavior of where males would go and spend their time - Control—reverse situation—put males in cages and track where females went - Tracking using radio telemetry- put radio collar- get estimate where males are going Diagram - dashed squares are cages where females were in - left are clumped ( more than one female in cage at a time) - dispersal on right- single females in single cage - polygon is some form of tracking of males - male is either between cages or around cages---- in clumped condition - females are dispersed ins some way and males spend time around in females - but in control---- SMHR instead of SFHR--- the movements of females deviate more from cages itself --- quantified difference between dispersal- males were 14X more likely to be located next to a cage than were females who were freely ranging - conclude- male dispersal is tightly linked to presence of females and female presence does not depend on males what so ever- so females looking for something else besides male presence - why would females choose polygymous or monogamous relationship What drives female decision- polygyny threshold model - female presented with choice--- choose male defending lone territory o male defending territory with single female present already - experiment- female make choice where she decided to mate with male—male settled in 4 different territory with variance in resource (e.g. food)—first female that arrives and choose territory on the one that provides optimal resources- therefore choose the male with site of most food - second female arrives- chooses and face landscape of first territory occupied by first female--- if she chooses that one, she has to share resource and food--- if that amount of food is still greater than the other territories, she should still choose the first piece of land- -- then she has passed polygyny threshold - but if second female settles on second site because she gets more food, the third female has to compare first and second most plentiful site which are occupied and see if that has more resources than the remaining land - make choices based on territory quality - better quality, better probability for fitness or reproductive success- females hsoudl be choosing higher quality territories— Graph - D is highest quality site--- in terms of fitness - A and C--- reproductive success of female choosing either site is the same PTM Example - first example of polygyny example model - resource that determine reproductive success is not food but shading—main cause of chicks in lark buntings is overheating - females often make decisions not on quality of food but the quality of shading in one env. Over a second env. --- females should go towards territory that has more shading--- - male provide some help to female to rear offspring---e.g. on a territory that already has a female, the second female that comes will be accepted and mated with male but male will only provide to primary female - so females have tough choice – good shade but male already has primary female V.S. worse shade but may get help from male Polygeny and decision theory - look at territory of male lark buntings - first graph is known distribution of sites – each outline is a territory and dots represent where females are not present and open areas are occupied by males and indicate at least one female present---- a monogamous site - centre shaded is at least two females present - second graph--- removed shading as much as possible and in dashed areas added artificial plants and see of those male territory holders, how many females did they get - shading reduced, get no mates and on edge there are some monogamous males and T and P represent polygamous relationship and this only happens in most shaded areas - females are sacrificing help for resources PTM - fails to acknowledge when 3 or 4 or 5 female has made their choice, does 1 change st their decision-reproductive success is affected by all those that comes after her - second assumption is hard to accomplish - third assumption- benefit with more than one f
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