7.3 OFFSPRING SIZE AND NUMBER STRAT

7.3 OFFSPRING SIZE AND NUMBER STRATEGIES

7.3.1 Theoretical context

Why do some fish, ranging phylogenetically from the sea lamprey (Petromyzon marinus, Cephalaspidomorpha) through the Atlantic sturgeon (Acipenser oxyrhynchus, Acipenseriformes) and the Atlantic cod (Gadus morhua, Gadiformes) to the sunfish (Mola mola, Tetraodontiformes),produce hundreds of thousands, often millions, of very small eggs (4mm diameter)?
The evolutionary implications of the trade-off between offspring number and offspring size in fish were first considered by the Swedish fish biologist Gunnar Svärdson (1949). He suggested that there must be an upper limit to fecundity and that this upper limit depends on the influence of egg size on offspring survival and parental reproductive success. Otherwise, he argued, directional selection – or, as he put it, a tendency to increase egg number every generation – would favour continually increased numbers of eggs per female. Svärdson (1949) remarked that, ‘From a theoretical point of view it is rather easy to conclude that there must be a selection pressure for decreasing egg numbers, but it is not so extremely evident how this selection works.’
The theoretical underpinning of most research investigating the adaptive significance of offspring size and number variability is a graphical model proposed by Smith and Fretwell (1974), who asked how a parent should distribute a fixed amount of energy or resources to an indeterminate number of young. Optimal egg size is defined graphically by the point on the fitness function at which a straight line drawn from the origin (the dashed lines in Fig. 7.1a) is tangential to the offspring survival curve (the solid curves in Fig. 7.1a). In other words, the optimum corresponds to the egg size at which the instantaneous rate of gain in fitness per unit increase in offspring size is at its maximum. As this instantaneous rate of gain increases, along with the slope of the line drawn from the origin, optimal egg size decreases (Winkler and Wallin 1987). Smith and Fretwell’s (1974) model has formed the basis of many theoretical treatments of the evolution of egg size, including those examining the effects of parental care (Sargent et al. 1987), food abundance (Hutchings 1991, 1997) and lifetime reproductive effort (Winkler and Wallin 1987).
Strong empirical support for Smith and Fretwell’s (1974) model was recently obtained from a study of Atlantic salmon egg size and maternal fitness (Einum and Fleming 2000).

7.3.2 How does egg size influence offspring survival?

At first glance, it might seem reasonable to assume that the larger the egg, the greater an offspring’s survival probability. Indeed there is considerable experimental evidence (Houde 1989; Pepin 1991, 1993; Chambers 1997; Wootton 1998) that larger offspring are produced from larger eggs, have increased survival during short periods of low food supply, can be more competitive than smaller offspring and, by virtue of their faster swimming speeds, may have a lower risk of predation. Fieldbased data have provided indirect evidence that survival in early life may be positively associated with size and individual growth rate at hatching, both of which are presumed positive correlates of egg size (Elliott 1994; Wootton 1998). Gronkjaer and Schytte (1999) reported that otolith hatchchecks of Baltic cod larvae that survived 20 days post-hatch were similar to or larger than the overall mean, suggesting an association between size at hatch and larval survival. Meekan and Fortier (1996) documented both positive and equivocal evidence that high individual growth rate enhances larval cod survival. Despite these potential benefits to fitness, larger egg sizes may impose constraints that negatively influence survival. For example, larger eggs can have longer development times (Kamler 1992) that prolong a potentially vulnerable period of life, greater oxygen demands (Kamler 1992; Quinn et al. 1995) and may, in addition to the young that emerge from them, be more visible to predators (Litvak and Leggett 1992; Pepin et al. 1992). Thus, the costs and benefits to offspring of emerging from large and small eggs can be expected to vary with a variety of factors, including the habitat into which eggs are released, such as being buried in substrate, attached to plants/rocks or dispersed freely into the water column, parental care, food supply and risk of detection by visual predators.

7.3.3 Hypotheses to explain variability in strategies of the size and number of offspring

Various hypotheses have been proposed to explain variation in egg size and fecundity within and among species of fish. Many adaptive explanations centre upon proposed selection responses to species- and age-specific differences in the quality of parental care (Sargent et al. 1987) and to seasonal (Rijnsdorp and Vingerhoed 1994; Trippel 1998), population (Kaplan and Cooper 1984; Hutchings 1991, 1997) and individual (Jonsson et al. 1996) differences in access to food resources. Quinn et al. (1995) suggested that among-population variation in sockeye salmon, Oncorhynchus nerka, egg size can be explained as adaptive responses to differences in the size composition of incubation gravel, arguing that the positive association between egg size and substrate size may be related to the latter’s influence on dissolved oxygen supplies relative to the surface-to-volume ratio constraints of eggs.
The reduction in egg mortality achieved by various forms of parental care, expressed in the form of burying of eggs, predator defence, mouthbrooding and egg fanning, is considered a primary selective factor responsible for the positive association between egg size and amount of parental care among species (Sargent et al. 1987; Forsgren et al., Chapter 10, this volume). Parental care may also offset the mortality costs associated with the longer developmental times of larger eggs. By extension, the positive association between egg size and maternal size documented within many fish species has been attributed to a greater ability of larger females to provide parental care to their young (Sargent et al. 1987). Larger females may be able to provide greater protection to eggs. However, the generality of this hypothesis must be tempered by the observation that egg size also increases with female size in fish that provide no parental care. This is shown by Atlantic cod (Chambers and Waiwood 1996; Kjesbu et al. 1996), Atlantic herring, Clupea harengus (Hempel and Blaxter 1967), caplin, Mallotus villosus (Chambers et al. 1989), and striped bass, Morone saxatilis (Zastrow et al. 1989).
Population differences in average egg size are often considered a proxy for adaptive variation. But, as previously noted elsewhere (Hutchings 1991; Reznick and Yang 1993), the relationship between offspring size and offspring survival must differ among environments, or among populations, for environment- or population-specific egg-size optima to exist (Fig. 7.1). Hutchings (1991) reported the first such phenotype x environment interaction on offspring survival in fish. Brook trout survival in the laboratory during the first 50 days following yolk-sac resorption was found to increase with egg size, but the effects of egg size and food abundance on juvenile survival were not additive: decreased food abundance increased mortality among juveniles from the smallest eggs but had no effect on the survival of juveniles produced from the largest eggs, a finding similar to that observed for brown trout (Einum and Fleming 1999). Based on these experimental data, and supported by field data on egg size and food abundance (Hutchings 1997), fitness functions described therefrom suggested that low food supply would favour the production of comparatively few, large offspring while high food abundance would favour females that produced many, comparatively small offspring (Hutchings 1991).
The dependence of environment-specific eggsize optima on the shape of the function relating offspring survival to egg size is illustrated in Fig. 7.1, where parental fitness (Fig. 7.1c,d) is approximated by the product of egg survival and egg number, holding gonad volume constant. Two basic functions are considered: the size-dependent case, for which offspring survival varies continuously with egg size (Fig. 7.1a), and the sizeindependent case, for which survival above and below a very narrow range of egg sizes is constant (Fig. 7.1b). For the former, any factor such as food supply that is expected to increase offspring survival across all egg sizes is predicted to effect a reduction in optimal egg size (Fig. 7.1a), thus favouring females that produce relatively numerous, smaller offspring (Fig. 7.1c). By contrast, if offspring survival is independent of offspring size, optimal egg size is predicted to remain unchanged with changes in a factor that increases offspring survival (Fig. 7.1d). Under such circumstances, the evolutionarily stable strategy of investment per offspring would appear to be one of maximizing the number of offspring, each approaching the physiologically minimum size, within a brood.
Given the within-individual trade-off that must exist between egg size and egg number for a specific gonadal volume, it is evident that for selection to favour an increase in egg size, the survival benefits to offspring produced from larger eggs must exceed the parental fitness cost of producing fewer eggs (Wootton 1994; Hutchings 1997). Unfortunately, explicit recognition of this necessity is notably rare in many discussions of egg-size optima, particularly in the marine fish literature. The fecundity cost associated with the production of large eggs must be acknowledged if natural variation in egg size in fish is to be interpreted within an ecological

Hasil (Bahasa Indonesia) 1:

7.3 OFFSPRING SIZE AND NUMBER STRATEGIES

7.3.1 Theoretical context

Why do some fish, ranging phylogenetically from the sea lamprey (Petromyzon marinus, Cephalaspidomorpha) through the Atlantic sturgeon (Acipenser oxyrhynchus, Acipenseriformes) and the Atlantic cod (Gadus morhua, Gadiformes) to the sunfish (Mola mola, Tetraodontiformes),produce hundreds of thousands, often millions, of very small eggs (<1.5mm diameter), while other fish, including myxinids, chondrichthyans, many salmoniforms and mouth-brooding siluriforms produce comparatively few, relatively large eggs (>4mm diameter)?
The evolutionary implications of the trade-off between offspring number and offspring size in fish were first considered by the Swedish fish biologist Gunnar Svärdson (1949). He suggested that there must be an upper limit to fecundity and that this upper limit depends on the influence of egg size on offspring survival and parental reproductive success. Otherwise, he argued, directional selection – or, as he put it, a tendency to increase egg number every generation – would favour continually increased numbers of eggs per female. Svärdson (1949) remarked that, ‘From a theoretical point of view it is rather easy to conclude that there must be a selection pressure for decreasing egg numbers, but it is not so extremely evident how this selection works.’
The theoretical underpinning of most research investigating the adaptive significance of offspring size and number variability is a graphical model proposed by Smith and Fretwell (1974), who asked how a parent should distribute a fixed amount of energy or resources to an indeterminate number of young. Optimal egg size is defined graphically by the point on the fitness function at which a straight line drawn from the origin (the dashed lines in Fig. 7.1a) is tangential to the offspring survival curve (the solid curves in Fig. 7.1a). In other words, the optimum corresponds to the egg size at which the instantaneous rate of gain in fitness per unit increase in offspring size is at its maximum. As this instantaneous rate of gain increases, along with the slope of the line drawn from the origin, optimal egg size decreases (Winkler and Wallin 1987). Smith and Fretwell’s (1974) model has formed the basis of many theoretical treatments of the evolution of egg size, including those examining the effects of parental care (Sargent et al. 1987), food abundance (Hutchings 1991, 1997) and lifetime reproductive effort (Winkler and Wallin 1987).
Strong empirical support for Smith and Fretwell’s (1974) model was recently obtained from a study of Atlantic salmon egg size and maternal fitness (Einum and Fleming 2000).

7.3.2 How does egg size influence offspring survival?

At first glance, it might seem reasonable to assume that the larger the egg, the greater an offspring’s survival probability. Indeed there is considerable experimental evidence (Houde 1989; Pepin 1991, 1993; Chambers 1997; Wootton 1998) that larger offspring are produced from larger eggs, have increased survival during short periods of low food supply, can be more competitive than smaller offspring and, by virtue of their faster swimming speeds, may have a lower risk of predation. Fieldbased data have provided indirect evidence that survival in early life may be positively associated with size and individual growth rate at hatching, both of which are presumed positive correlates of egg size (Elliott 1994; Wootton 1998). Gronkjaer and Schytte (1999) reported that otolith hatchchecks of Baltic cod larvae that survived 20 days post-hatch were similar to or larger than the overall mean, suggesting an association between size at hatch and larval survival. Meekan and Fortier (1996) documented both positive and equivocal evidence that high individual growth rate enhances larval cod survival. Despite these potential benefits to fitness, larger egg sizes may impose constraints that negatively influence survival. For example, larger eggs can have longer development times (Kamler 1992) that prolong a potentially vulnerable period of life, greater oxygen demands (Kamler 1992; Quinn et al. 1995) and may, in addition to the young that emerge from them, be more visible to predators (Litvak and Leggett 1992; Pepin et al. 1992). Thus, the costs and benefits to offspring of emerging from large and small eggs can be expected to vary with a variety of factors, including the habitat into which eggs are released, such as being buried in substrate, attached to plants/rocks or dispersed freely into the water column, parental care, food supply and risk of detection by visual predators.

7.3.3 Hypotheses to explain variability in strategies of the size and number of offspring

Various hypotheses have been proposed to explain variation in egg size and fecundity within and among species of fish. Many adaptive explanations centre upon proposed selection responses to species- and age-specific differences in the quality of parental care (Sargent et al. 1987) and to seasonal (Rijnsdorp and Vingerhoed 1994; Trippel 1998), population (Kaplan and Cooper 1984; Hutchings 1991, 1997) and individual (Jonsson et al. 1996) differences in access to food resources. Quinn et al. (1995) suggested that among-population variation in sockeye salmon, Oncorhynchus nerka, egg size can be explained as adaptive responses to differences in the size composition of incubation gravel, arguing that the positive association between egg size and substrate size may be related to the latter’s influence on dissolved oxygen supplies relative to the surface-to-volume ratio constraints of eggs.
The reduction in egg mortality achieved by various forms of parental care, expressed in the form of burying of eggs, predator defence, mouthbrooding and egg fanning, is considered a primary selective factor responsible for the positive association between egg size and amount of parental care among species (Sargent et al. 1987; Forsgren et al., Chapter 10, this volume). Parental care may also offset the mortality costs associated with the longer developmental times of larger eggs. By extension, the positive association between egg size and maternal size documented within many fish species has been attributed to a greater ability of larger females to provide parental care to their young (Sargent et al. 1987). Larger females may be able to provide greater protection to eggs. However, the generality of this hypothesis must be tempered by the observation that egg size also increases with female size in fish that provide no parental care. This is shown by Atlantic cod (Chambers and Waiwood 1996; Kjesbu et al. 1996), Atlantic herring, Clupea harengus (Hempel and Blaxter 1967), caplin, Mallotus villosus (Chambers et al. 1989), and striped bass, Morone saxatilis (Zastrow et al. 1989).
Population differences in average egg size are often considered a proxy for adaptive variation. But, as previously noted elsewhere (Hutchings 1991; Reznick and Yang 1993), the relationship between offspring size and offspring survival must differ among environments, or among populations, for environment- or population-specific egg-size optima to exist (Fig. 7.1). Hutchings (1991) reported the first such phenotype x environment interaction on offspring survival in fish. Brook trout survival in the laboratory during the first 50 days following yolk-sac resorption was found to increase with egg size, but the effects of egg size and food abundance on juvenile survival were not additive: decreased food abundance increased mortality among juveniles from the smallest eggs but had no effect on the survival of juveniles produced from the largest eggs, a finding similar to that observed for brown trout (Einum and Fleming 1999). Based on these experimental data, and supported by field data on egg size and food abundance (Hutchings 1997), fitness functions described therefrom suggested that low food supply would favour the production of comparatively few, large offspring while high food abundance would favour females that produced many, comparatively small offspring (Hutchings 1991).
The dependence of environment-specific eggsize optima on the shape of the function relating offspring survival to egg size is illustrated in Fig. 7.1, where parental fitness (Fig. 7.1c,d) is approximated by the product of egg survival and egg number, holding gonad volume constant. Two basic functions are considered: the size-dependent case, for which offspring survival varies continuously with egg size (Fig. 7.1a), and the sizeindependent case, for which survival above and below a very narrow range of egg sizes is constant (Fig. 7.1b). For the former, any factor such as food supply that is expected to increase offspring survival across all egg sizes is predicted to effect a reduction in optimal egg size (Fig. 7.1a), thus favouring females that produce relatively numerous, smaller offspring (Fig. 7.1c). By contrast, if offspring survival is independent of offspring size, optimal egg size is predicted to remain unchanged with changes in a factor that increases offspring survival (Fig. 7.1d). Under such circumstances, the evolutionarily stable strategy of investment per offspring would appear to be one of maximizing the number of offspring, each approaching the physiologically minimum size, within a brood.
Given the within-individual trade-off that must exist between egg size and egg number for a specific gonadal volume, it is evident that for selection to favour an increase in egg size, the survival benefits to offspring produced from larger eggs must exceed the parental fitness cost of producing fewer eggs (Wootton 1994; Hutchings 1997). Unfortunately, explicit recognition of this necessity is notably rare in many discussions of egg-size optima, particularly in the marine fish literature. The fecundity cost associated with the production of large eggs must be acknowledged if natural variation in egg size in fish is to be interpreted within an ecological

Hasil (Bahasa Indonesia) 2:

7.3 keturunan UKURAN DAN JUMLAH STRATEGI 7.3.1 konteks teoritis Mengapa beberapa ikan, mulai filogenetis dari lamprey laut (Petromyzon marinus, Cephalaspidomorpha) melalui sturgeon Atlantik (Acipenser Oxyrhynchus, Acipenseriformes) dan Atlantik cod (Gadus morhua, Gadiformes) ke sunfish (Mola mola, Tetraodontiformes), menghasilkan ratusan ribu, jutaan sering, telur yang sangat kecil (<diameter 1.5mm), sedangkan ikan lain, termasuk myxinids, chondrichthyans, banyak salmoniforms dan mulut-merenung siluriforms menghasilkan relatif sedikit, telur relatif besar (> diameter 4mm)? Implikasi evolusi trade-off antara jumlah keturunan dan ukuran keturunan ikan pertama kali dianggap oleh Swedia ikan biologi Gunnar Svärdson (1949). Dia menyarankan bahwa harus ada batas atas untuk fekunditas dan batas atas ini tergantung pada pengaruh ukuran telur pada kelangsungan hidup keturunan dan keberhasilan reproduksi orangtua. Jika tidak, ia berpendapat, arah seleksi - atau, seperti yang ia katakan, kecenderungan untuk meningkatkan jumlah telur setiap generasi - akan mendukung terus meningkatnya jumlah telur per betina. Svärdson (1949) mengatakan bahwa, "Dari sudut pandang teoritis itu agak mudah untuk menyimpulkan bahwa harus ada tekanan seleksi untuk mengurangi jumlah telur, tapi tidak begitu sangat jelas bagaimana seleksi ini bekerja." Yang mendasari teori paling penelitian yang menyelidiki pentingnya adaptif ukuran keturunan dan variabilitas nomor adalah model grafis yang diusulkan oleh Smith dan Fretwell (1974), yang bertanya bagaimana orangtua harus mendistribusikan jumlah tetap energi atau sumber daya untuk jumlah tak tentu muda. Ukuran telur yang optimal didefinisikan grafis oleh titik pada fungsi fitness di mana garis lurus yang ditarik dari asal (garis putus-putus dalam 7.1a Gambar.) Adalah tangensial dengan kurva keturunan survival (kurva solid dalam 7.1a Gambar.). Dengan kata lain, optimal sesuai dengan ukuran telur di mana tingkat seketika keuntungan dalam kebugaran per unit peningkatan ukuran anak berada pada maksimum. Sebagai tingkat ini seketika keuntungan meningkat, seiring dengan kemiringan garis yang ditarik dari asal, ukuran telur yang optimal menurun (Winkler dan Wallin 1987). Smith dan Fretwell (1974) Model telah membentuk dasar dari banyak perawatan teoritis evolusi ukuran telur, termasuk yang menguji efek pengasuhan (Sargent et al. 1987), kelimpahan makanan (Hutchings 1991, 1997) dan masa usaha reproduksi (Winkler dan Wallin 1987). Kuat dukungan empiris untuk Smith dan Fretwell (1974) Model baru-baru ini diperoleh dari studi Atlantik ukuran salmon telur dan kebugaran ibu (Einum dan Fleming 2000). 7.3.2 Bagaimana ukuran telur pengaruh keturunan bertahan hidup? Pada pandangan pertama, mungkin tampak masuk akal untuk mengasumsikan bahwa semakin besar telur, semakin besar probabilitas kelangsungan hidup keturunan itu. Memang ada bukti eksperimental yang cukup (Houde 1989; Pepin 1991, 1993; Chambers 1997; Wootton 1998) bahwa keturunan yang lebih besar yang dihasilkan dari telur yang lebih besar, telah meningkatkan angka harapan hidup selama periode singkat pasokan makanan rendah, bisa lebih kompetitif daripada keturunan yang lebih kecil dan, berdasarkan kecepatan berenang lebih cepat, mungkin memiliki risiko lebih rendah dari predasi. Data Fieldbased telah memberikan bukti tidak langsung bahwa kelangsungan hidup pada awal kehidupan dapat secara positif dengan ukuran dan tingkat pertumbuhan individu pada penetasan, yang keduanya diduga berkorelasi positif dengan ukuran telur (Elliott 1994; Wootton 1998). Gronkjaer dan Schytte (1999) melaporkan bahwa hatchchecks otolith larva cod Baltik yang selamat 20 hari pasca-menetas mirip dengan atau lebih besar dari rata-rata keseluruhan, menunjukkan hubungan antara ukuran di hatch dan kelangsungan hidup larva. Meekan dan Fortier (1996) mendokumentasikan bukti positif dan samar-samar bahwa tingkat pertumbuhan individu yang tinggi meningkatkan cod kelangsungan hidup larva. Meskipun manfaat potensi untuk kebugaran, ukuran telur yang lebih besar dapat mengenakan kendala yang negatif mempengaruhi kelangsungan hidup. Misalnya, telur yang lebih besar dapat memiliki waktu pengembangan lebih lama (Kamler 1992) yang memperpanjang masa berpotensi rentan kehidupan, kebutuhan oksigen yang lebih besar (Kamler 1992;. Quinn et al 1995) dan mungkin, di samping muda yang muncul dari mereka, menjadi lebih terlihat predator (Litvak dan Leggett 1992; Pepin et al 1992.). Dengan demikian, biaya dan manfaat bagi keturunan muncul dari telur besar dan kecil dapat diharapkan untuk bervariasi dengan berbagai faktor, termasuk habitat di mana telur dilepaskan, seperti dimakamkan di substrat, yang melekat pada tanaman / batu atau tersebar bebas ke dalam kolom air, pengasuhan, pasokan makanan dan risiko deteksi oleh predator visual. 7.3.3 Hipotesis untuk menjelaskan variabilitas dalam strategi ukuran dan jumlah keturunan Berbagai hipotesis telah diajukan untuk menjelaskan variasi dalam ukuran telur dan fekunditas dalam dan di antara spesies ikan. Banyak penjelasan adaptif pusat pada respon seleksi yang diusulkan untuk speciesnya dan perbedaan usia tertentu dalam kualitas pengasuhan (Sargent et al 1987.) Dan musiman (Rijnsdorp dan Vingerhoed 1994; Trippel 1998), penduduk (Kaplan dan Cooper 1984; Hutchings 1991, 1997) dan individu (Jonsson et al. 1996) perbedaan dalam akses terhadap sumber daya pangan. Quinn et al. (1995) mengemukakan bahwa di antara populasi variasi sockeye salmon, Oncorhynchus nerka, ukuran telur dapat dijelaskan sebagai respon adaptif terhadap perbedaan dalam komposisi ukuran inkubasi kerikil, dengan alasan bahwa hubungan positif antara ukuran telur dan ukuran substrat mungkin berhubungan dengan pengaruh pada pasokan oksigen terlarut relatif terhadap permukaan-ke-volume kendala rasio telur terakhir. Penurunan angka kematian telur dicapai dengan berbagai bentuk pengasuhan, dinyatakan dalam bentuk mengubur telur, pertahanan predator, mouthbrooding dan mengipasi telur, adalah dianggap sebagai faktor utama selektif bertanggung jawab atas hubungan positif antara ukuran telur dan jumlah pengasuhan antara spesies (Sargent et al 1987;.. Forsgren et al, Bab 10 buku ini). Pengasuhan juga dapat mengimbangi biaya kematian terkait dengan kali lebih lama perkembangan telur yang lebih besar. Dengan ekstensi, hubungan positif antara ukuran telur dan ukuran ibu didokumentasikan dalam banyak spesies ikan telah dikaitkan dengan kemampuan yang lebih dari perempuan yang lebih besar untuk memberikan perawatan orangtua untuk anak-anak mereka (Sargent et al. 1987). Betina lebih besar mungkin dapat memberikan perlindungan yang lebih besar untuk telur. Namun, keumuman hipotesis ini harus marah oleh pengamatan bahwa ukuran telur juga meningkat dengan ukuran perempuan pada ikan yang tidak memberikan pengasuhan. Hal ini ditunjukkan dengan Atlantic cod (Chambers dan Waiwood 1996; Kjesbu et al 1996.), Herring Atlantik, Clupea harengus (Hempel dan Blaxter 1967), Caplin, Mallotus villosus (Chambers et al 1989.), Dan striped bass, Morone saxatilis ( Zastrow et al. 1989). Perbedaan Populasi dalam ukuran rata-rata telur sering dianggap proxy untuk variasi adaptif. Tapi, seperti sebelumnya dicatat di tempat lain (Hutchings 1991; Reznick dan Yang 1993), hubungan antara ukuran keturunan dan keturunan hidup harus berbeda antara lingkungan, atau di antara populasi, untuk lingkungan-atau-populasi tertentu telur ukuran optima ada (Gambar 7.1. ). Hutchings (1991) melaporkan pertama seperti fenotipe x lingkungan interaksi pada kelangsungan hidup keturunan ikan. Brook trout hidup di laboratorium selama 50 hari pertama setelah kuning-sac resorpsi ditemukan meningkat dengan ukuran telur, tetapi efek dari ukuran telur dan makanan berlimpah pada kelangsungan hidup remaja tidak aditif: penurunan kelimpahan makanan peningkatan mortalitas di antara remaja dari yang terkecil telur tapi tidak berpengaruh pada kelangsungan hidup remaja yang dihasilkan dari telur terbesar, yang menemukan mirip dengan yang diamati untuk ikan trout coklat (Einum dan Fleming 1999). Berdasarkan data-data eksperimen, dan didukung oleh data lapangan pada ukuran telur dan kelimpahan makanan (Hutchings 1997), fungsi fitness digambarkan darinya menyarankan bahwa persediaan makanan yang rendah akan mendukung produksi relatif sedikit, keturunan besar sementara kelimpahan pangan yang tinggi akan mendukung perempuan yang dihasilkan banyak, keturunan relatif kecil (Hutchings 1991). Ketergantungan lingkungan spesifik eggsize optima pada bentuk fungsi yang berkaitan keturunan bertahan hidup dengan ukuran telur diilustrasikan pada Gambar. 7.1, di mana (7.1c Gambar., D) kebugaran orangtua didekati oleh produk kelangsungan hidup telur dan nomor telur, memegang Volume gonad konstan. Dua fungsi dasar dianggap: kasus tergantung ukuran, yang keturunan bertahan hidup bervariasi terus menerus dengan ukuran telur (Gambar 7.1a.), Dan kasus sizeindependent, yang bertahan hidup di atas dan di bawah rentang yang sangat sempit ukuran telur adalah konstan (Gambar . 7.1b). Untuk yang pertama, faktor apa saja seperti persediaan makanan yang diharapkan dapat meningkatkan kelangsungan hidup anak di semua ukuran telur diperkirakan mempengaruhi penurunan ukuran telur optimal (Gambar. 7.1a), sehingga mendukung betina yang menghasilkan relatif banyak, keturunan yang lebih kecil (Gambar . 7.1c). Sebaliknya, jika anak hidup tidak tergantung pada ukuran keturunan, ukuran telur yang optimal diperkirakan tetap tidak berubah dengan perubahan faktor yang meningkatkan keturunan bertahan hidup (Gambar. 7.1d). Dalam keadaan seperti itu, strategi evolusi yang stabil investasi per anak akan muncul menjadi salah satu memaksimalkan jumlah anak, masing-masing mendekati ukuran fisiologis minimum, dalam merenung a. Mengingat dalam-individu trade-off yang harus ada antara ukuran telur dan Jumlah telur untuk volume gonad tertentu, jelas bahwa untuk seleksi untuk mendukung peningkatan ukuran telur, manfaat kelangsungan hidup keturunan yang dihasilkan dari telur yang lebih besar harus melebihi biaya orangtua kebugaran memproduksi telur yang lebih sedikit (Wootton 1994; Hutchings 1997). Sayangnya, pengakuan eksplisit dari kebutuhan ini terutama langka di banyak diskusi telur ukuran optima, khususnya dalam literatur ikan laut. Biaya Fekunditas terkait dengan produksi telur yang besar harus diakui jika variasi alami dalam ukuran telur ikan harus ditafsirkan dalam suatu ekologi