45.2: Historia ya Maisha na Uchaguzi wa Asili

Ujuzi wa Kuendeleza

• Eleza jinsi mifumo ya historia ya maisha inavyoathiriwa na uteuzi wa asili
• Eleza mifumo tofauti ya historia ya maisha na jinsi mikakati tofauti ya uzazi inavyoathiri maisha ya aina

Historia ya maisha ya aina inaelezea mfululizo wa matukio katika maisha yake, kama vile jinsi rasilimali zinazotengwa kwa ajili ya ukuaji, matengenezo, na uzazi. Tabia za historia ya maisha huathiri meza ya maisha ya viumbe. Historia ya maisha ya aina ni vinasaba kuamua na umbo na mazingira na uteuzi asili.

Historia ya Maisha Sampuli na Nishati

Nishati inahitajika na viumbe hai vyote kwa ajili ya ukuaji wao, matengenezo, na uzazi wao; wakati huo huo, nishati mara nyingi ni sababu kubwa ya kuzuia katika kuamua maisha ya kiumbe. Mimea, kwa mfano, hupata nishati kutoka jua kupitia usanisinuru, lakini lazima itumie nishati hii kukua, kudumisha afya, na kuzalisha mbegu zenye nishati kuzalisha kizazi kijacho. Wanyama wana mzigo wa ziada wa kutumia baadhi ya akiba zao za nishati ili kupata chakula. Aidha, baadhi ya wanyama lazima expend nishati ya kutunza watoto wao. Hivyo, aina zote zina bajeti ya nishati: zinapaswa kusawazisha ulaji wa nishati na matumizi yao ya nishati kwa kimetaboliki, uzazi, huduma ya wazazi, na hifadhi ya nishati (kama vile huzaa kujenga mafuta ya mwili kwa majira ya baridi hibernation).

Huduma ya Wazazi na Uzazi

Fecundity ni uwezo wa uzazi wa mtu binafsi ndani ya idadi ya watu. Kwa maneno mengine, fecundity inaelezea jinsi watoto wengi wanaweza kuzalishwa kama mtu ana watoto wengi iwezekanavyo, kurudia mzunguko wa uzazi haraka iwezekanavyo baada ya kuzaliwa kwa watoto. Katika wanyama, fecundity inahusiana na kiasi cha huduma ya wazazi iliyotolewa kwa watoto binafsi. Spishi, kama vile uti wa mgongo wengi wa baharini, ambao huzalisha watoto wengi kwa kawaida hutoa huduma kidogo kama yoyote kwa watoto (wasingekuwa na nishati au uwezo wa kufanya hivyo hata hivyo). Wengi wa bajeti yao ya nishati hutumiwa kuzalisha watoto wengi wadogo. Wanyama wenye mkakati huu mara nyingi wanajitosheleza katika umri mdogo sana. Hii ni kwa sababu ya biashara ya nishati viumbe hawa wamefanya ili kuongeza fitness yao ya mabadiliko. Kwa sababu nishati yao hutumiwa kuzalisha watoto badala ya utunzaji wa wazazi, ni mantiki kwamba watoto hawa wana uwezo fulani wa kuhamia ndani ya mazingira yao na kupata chakula na labda makazi. Hata kwa uwezo huu, ukubwa wao mdogo huwafanya kuwa hatari sana kwa uharibifu, hivyo uzalishaji wa watoto wengi huwawezesha kutosha kuishi ili kudumisha aina.

Aina za wanyama ambazo zina watoto wachache wakati wa tukio la uzazi hutoa huduma kubwa ya wazazi, wakitoa bajeti kubwa ya nishati kwa shughuli hizi, wakati mwingine kwa gharama ya afya zao wenyewe. Hii ni kesi kwa mamalia wengi, kama vile binadamu, kangaroos, na pandas. Watoto wa aina hizi hawana msaada wakati wa kuzaliwa na wanahitaji kuendeleza kabla ya kufikia kujitegemea.

Mimea yenye fecundity ndogo huzalisha mbegu chache tajiri za nishati (kama vile nazi na chestnuts) huku kila mmoja ana nafasi nzuri ya kuota ndani ya viumbe vipya; mimea yenye fecundity ya juu huwa na mbegu nyingi ndogo, zenye nishati duni (kama orchidi) ambazo zina nafasi duni kiasi ya kuishi. Ingawa inaweza kuonekana kwamba nazi na chestnuts zina nafasi nzuri ya kuishi, biashara ya nishati ya orchid pia inafaa sana. Ni suala la wapi nishati hutumiwa, kwa idadi kubwa ya mbegu au kwa mbegu chache zilizo na nishati zaidi.

Mapema dhidi ya Uzazi Marehemu

Muda wa uzazi katika historia ya maisha pia huathiri maisha ya aina. Viumbe vinavyozalisha wakati wa umri mdogo vina nafasi kubwa ya kuzalisha watoto, lakini hii ni kawaida kwa gharama ya ukuaji wao na matengenezo ya afya zao. Kinyume chake, viumbe vinavyoanza kuzaliana baadaye katika maisha mara nyingi huwa na uzazi mkubwa au wana uwezo wa kutoa huduma za wazazi, lakini huhatarisha kuwa hawataishi hadi umri wa uzazi. Mifano ya hii inaweza kuonekana katika samaki. Samaki wadogo kama guppies hutumia nishati zao kuzaliana haraka, lakini kamwe kufikia ukubwa ambao utawapa utetezi dhidi ya baadhi ya wadudu. Samaki wakubwa, kama bluegill au shark, hutumia nishati yao ili kufikia ukubwa mkubwa, lakini fanya hivyo kwa hatari ya kuwa watakufa kabla ya kuzaa au angalau kuzaliana hadi kiwango cha juu. Mikakati hii tofauti ya nishati na biashara ni muhimu kuelewa mageuzi ya kila aina kama inavyoongeza fitness yake na hujaza niche yake. Kwa upande wa bajeti ya nishati, baadhi ya spishi “hupiga yote” na hutumia zaidi ya akiba zao za nishati kuzaliana mapema kabla ya kufa. Aina nyingine huchelewesha kuwa na uzazi ili kuwa na nguvu, watu wenye ujuzi zaidi na kuhakikisha kuwa wana nguvu ya kutosha kutoa huduma ya wazazi ikiwa ni lazima.

Single dhidi ya Matukio mengi ya Uzazi

Baadhi ya sifa za historia ya maisha, kama vile fecundity, muda wa uzazi, na huduma ya wazazi, zinaweza kuunganishwa pamoja katika mikakati ya jumla ambayo hutumiwa na aina nyingi. Semelparity hutokea wakati spishi huzaa mara moja tu wakati wa maisha yake halafu hufa. Aina hizo hutumia bajeti yao ya rasilimali wakati wa tukio moja la uzazi, kutoa dhabihu afya zao kwa uhakika kwamba hawaishi. Mifano ya semelpariity ni mianzi, ambayo maua mara moja na kisha kufa, na samaki ya Chinook (Kielelezo\(\PageIndex{1}\) a), ambayo hutumia zaidi ya hifadhi yake ya nishati kuhamia kutoka bahari hadi eneo lake la maji safi, ambako huzalisha na kisha kufa. Wanasayansi posited maelezo mbadala kwa faida ya mabadiliko ya kifo baada ya uzazi Chinook: iliyowekwa kujiua unasababishwa na kutolewa mkubwa wa homoni corticosteroid, labda hivyo wazazi wanaweza kuwa chakula kwa ajili ya watoto, au uchovu rahisi unasababishwa na mahitaji ya nishati ya uzazi; haya bado yanajadiliwa.

Iteroparity inaelezea aina zinazozalisha mara kwa mara wakati wa maisha yao. Wanyama wengine wana uwezo wa mate mara moja kwa mwaka, lakini wanaishi misimu mingi ya kuunganisha. Antelope ya pronghorn ni mfano wa mnyama anayeingia katika mzunguko wa msimu wa estrus (“joto”): hali ya kisaikolojia inayotokana na homoni inayoandaa mwili kwa kuunganisha mafanikio (Kielelezo\(\PageIndex{1}\) b). Wanawake wa aina hizi mate tu wakati wa awamu ya estrus ya mzunguko. Mfano tofauti huzingatiwa katika nyani, ikiwa ni pamoja na binadamu na sokwe, ambayo inaweza kujaribu uzazi wakati wowote wakati wa miaka yao ya uzazi, ingawa mzunguko wao wa hedhi hufanya mimba uwezekano wa siku chache tu kwa mwezi wakati wa ovulation (Kielelezo\(\PageIndex{1}\) c).

a

b

c

Kielelezo\(\PageIndex{1}\): the (a) Chinook samaki wenzi mara moja na kufa. Wa (b) wenzi wa antelope wakati wa nyakati maalum za mwaka wakati wa maisha yake ya uzazi. Primates, kama vile binadamu na (c) sokwe, inaweza mate siku yoyote, huru ya ovulation. (mikopo a: mabadiliko ya kazi na Roger Tabor, USFWS; mikopo b: mabadiliko ya kazi na Mark Gocke, USDA; mikopo c: mabadiliko ya kazi na “Mambo ya Shiny” /Flickr)

Evolution Connection: Bajeti ya Nishati, Gharama za Uzazi, na Uchaguzi wa Kingono

Utafiti wa jinsi wanyama wanavyotenga rasilimali zao za nishati kwa ajili ya ukuaji, matengenezo, na uzazi umetumia aina mbalimbali za mifano ya wanyama wa majaribio. Baadhi ya kazi hii imefanywa kwa kutumia kuruka kwa matunda ya kawaida, Drosophila melanogaster. Uchunguzi umeonyesha kuwa sio tu uzazi una gharama kwa muda gani wa nzizi za kiume wanaishi, lakini pia nzizi za matunda ambazo tayari zimeunganishwa mara kadhaa zina mbegu ndogo iliyobaki kwa uzazi. Matunda nzi kuongeza nafasi yao ya mwisho katika uzazi kwa kuchagua mates mojawapo.

Katika utafiti wa 1981, nzizi za kiume za matunda ziliwekwa katika vifungo na wanawake wa bikira au wasio na wanawake. wanaume kwamba mated na wanawake bikira alikuwa mfupi maisha spans kuliko wale katika kuwasiliana na idadi sawa ya wanawake inseminated na ambayo hawakuweza mate. Athari hii ilitokea bila kujali jinsi kubwa (dalili ya umri wao) wanaume walikuwa. Hivyo, wanaume ambao hawakuwa na mate waliishi muda mrefu, wakiwawezesha fursa zaidi za kupata wenzi katika siku zijazo.

Tafiti za hivi karibuni zaidi, zilizofanyika mwaka 2006, zinaonyesha jinsi wanaume wanavyochagua kike na ambayo watakuwa mate na jinsi hii inathiriwa na matings ya awali (Kielelezo\(\PageIndex{2}\)).¹ Males were allowed to select between smaller and larger females. Findings showed that larger females had greater fecundity, producing twice as many offspring per mating as the smaller females did. Males that had previously mated, and thus had lower supplies of sperm, were termed “resource-depleted,” while males that had not mated were termed “non-resource-depleted.” The study showed that although non-resource-depleted males preferentially mated with larger females, this selection of partners was more pronounced in the resource-depleted males. Thus, males with depleted sperm supplies, which were limited in the number of times that they could mate before they replenished their sperm supply, selected larger, more fecund females, thus maximizing their chances for offspring. This study was one of the first to show that the physiological state of the male affected its mating behavior in a way that clearly maximizes its use of limited reproductive resources.

Figure \(\PageIndex{2}\): Male fruit flies that had previously mated (sperm-depleted) picked larger, more fecund females more often than those that had not mated (non-sperm-depleted). This change in behavior causes an increase in the efficiency of a limited reproductive resource: sperm.

These studies demonstrate two ways in which the energy budget is a factor in reproduction. First, energy expended on mating may reduce an animal’s lifespan, but by this time they have already reproduced, so in the context of natural selection this early death is not of much evolutionary importance. Second, when resources such as sperm (and the energy needed to replenish it) are low, an organism’s behavior can change to give them the best chance of passing their genes on to the next generation. These changes in behavior, so important to evolution, are studied in a discipline known as behavioral biology, or ethology, at the interface between population biology and psychology.

Summary

All species have evolved a pattern of living, called a life history strategy, in which they partition energy for growth, maintenance, and reproduction. These patterns evolve through natural selection; they allow species to adapt to their environment to obtain the resources they need to successfully reproduce. There is an inverse relationship between fecundity and parental care. A species may reproduce early in life to ensure surviving to a reproductive age or reproduce later in life to become larger and healthier and better able to give parental care. A species may reproduce once (semelparity) or many times (iteroparity) in its life.

Footnotes

1. 1 Adapted from Phillip G. Byrne and William R. Rice, “Evidence for adaptive male mate choice in the fruit fly Drosophila melanogaster,” Proc Biol Sci. 273, no. 1589 (2006): 917-922, doi: 10.1098/rspb.2005.3372.

Glossary

energy budget

allocation of energy resources for body maintenance, reproduction, and parental care

fecundity

potential reproductive capacity of an individual

iteroparity

life history strategy characterized by multiple reproductive events during the lifetime of a species

life history

inherited pattern of resource allocation under the influence of natural selection and other evolutionary forces

semelparity

life history strategy characterized by a single reproductive event followed by death