Reproduction
Reproduction is the biological process by which parent organisms produce new individual organisms, thereby ensuring the continuity of genetic lineages and species propagation; it manifests primarily through asexual mechanisms, where a single parent generates genetically identical offspring, or sexual mechanisms, involving the fusion of specialized gametes from two parents to yield genetically diverse progeny.[1][2]
Asexual reproduction enables swift proliferation and colonization in stable environments, as offspring inherit the full parental genome without recombination, though it limits adaptability by accumulating deleterious mutations over generations—a phenomenon known as Muller's ratchet.[2][3]
In contrast, sexual reproduction predominates among eukaryotes, with over 99.99% engaging in it periodically, as meiosis and syngamy shuffle alleles, purging harmful mutations and fostering variation that bolsters survival amid fluctuating selective pressures.[3][4]
This duality underscores reproduction's pivotal role in evolution: asexual modes prioritize quantity for immediate expansion, while sexual modes emphasize quality through diversity, driving long-term resilience and speciation despite the twofold cost of males in dioecious systems.[5][3]
Fundamentals of Reproduction
Definition and Biological Scope
Reproduction is the biological process by which organisms generate new individuals capable of perpetuating their genetic material, a hallmark distinguishing living systems from non-living matter. This process occurs across all domains of life—Bacteria, Archaea, and Eukarya—encompassing both unicellular and multicellular forms, but excludes entities like viruses that require host machinery for propagation.[6][7] In prokaryotes, such as bacteria, reproduction primarily manifests as asexual binary fission, where a single parent cell divides into two genetically identical daughters via DNA replication and cytoplasmic partitioning, enabling rapid population growth under favorable conditions.[8] The biological scope of reproduction extends to diverse mechanisms tailored to organismal complexity and environment. In eukaryotes, asexual reproduction includes mitosis-driven processes like budding in yeast or fragmentation in certain algae and invertebrates, yielding clones that preserve parental genotypes. Sexual reproduction, involving meiosis and gamete fusion, introduces genetic recombination and variation, observed in taxa from fungi (via spore formation) to plants (alternation of generations) and animals (oogenesis and spermatogenesis leading to zygote formation). This duality allows adaptation: asexual modes favor efficiency in stable niches, while sexual modes enhance resilience against parasites and environmental shifts through heterozygote advantage and outcrossing. Empirical studies confirm reproduction's universality, with no known living taxon lacking propagative capacity at the population level, though individual sterility (e.g., hybrid mules or aging humans) occurs without negating species-level persistence.[8][9]Cellular Foundations: Mitosis and Meiosis
Mitosis is a form of eukaryotic cell division that produces two genetically identical diploid daughter cells from a single diploid parent cell, preserving the chromosome number (2n).[10] This process occurs in somatic cells and supports asexual reproduction by enabling the clonal propagation of organisms, as seen in mechanisms like binary fission in single-celled eukaryotes or fragmentation in multicellular forms such as starfish, where offspring inherit exact genetic copies of the parent.[11] Mitosis proceeds through four main phases—prophase (chromosome condensation and spindle formation), metaphase (chromosome alignment at the equator), anaphase (sister chromatid separation), and telophase (nuclear reformation)—followed by cytokinesis to divide the cytoplasm.[12] In reproductive contexts, mitosis facilitates the growth of multicellular structures from a single zygote or propagule in asexual lineages, ensuring rapid population expansion without genetic recombination. Meiosis, by contrast, is a specialized division in germ cells that yields four non-identical haploid (n) gametes from one diploid precursor, halving the chromosome count to prevent doubling upon fertilization.[13] Essential for sexual reproduction, it generates sperm and eggs (or equivalent gametes) in animals and plants, with meiosis I reducing ploidy via homologous chromosome pairing and separation, and meiosis II resembling mitosis to split sister chromatids.[14] Genetic diversity arises from crossing over (recombination between homologs) during prophase I and independent assortment of chromosomes at metaphase I, shuffling alleles to produce variable progeny upon gamete fusion.[15] This variability underpins evolutionary adaptation in sexual species, as fertilization merges two haploid sets to restore diploidy while introducing novel combinations.[16]| Aspect | Mitosis | Meiosis |
|---|---|---|
| Divisions | One | Two (meiosis I and II) |
| Daughter Cells | 2 diploid, genetically identical | 4 haploid, genetically diverse |
| Chromosome Number | Maintains 2n | Reduces from 2n to n |
| Role in Reproduction | Asexual (clonal offspring) | Sexual (gamete production) |
| Variation Mechanism | None (exact replication) | Crossing over and independent assortment |
Asexual Reproduction
Primary Mechanisms
Binary fission is a primary mechanism of asexual reproduction in prokaryotes such as bacteria and archaea, where the parent cell replicates its DNA and divides into two genetically identical daughter cells.[18] This process occurs rapidly under favorable conditions, enabling exponential population growth; for instance, Escherichia coli can divide every 20 minutes in optimal laboratory settings.[19] Budding involves the formation of a small outgrowth or bud on the parent organism, which develops into a new individual that eventually separates. This mechanism is observed in unicellular eukaryotes like yeast (Saccharomyces cerevisiae), where the bud forms from mitotic division and nuclear migration, and in multicellular organisms such as freshwater hydra, where the bud arises from epithelial and interstitial cells. The resulting offspring are clones of the parent, though cytoplasmic inheritance may introduce minor variations.[19] Fragmentation entails the breakage of the parent body into multiple pieces, each of which regenerates into a complete organism via mitotic cell division. Common in elongated or modular organisms, this occurs in starfish (where a severed arm can regrow the entire body) and planarian flatworms, which rely on neoblasts—undifferentiated stem cells—for regeneration.[18] Environmental stressors like injury often trigger fragmentation, ensuring survival through dispersal of propagules.[19] Parthenogenesis is the development of an unfertilized egg into a viable offspring, producing clones that are diploid through mechanisms like automixis or apomixis. This facultative or obligate process appears in arthropods such as aphids (which switch to parthenogenesis during resource abundance, yielding up to 100 generations without males) and certain vertebrates including Whiptail lizards (Aspidoscelis spp.), where all individuals are female and offspring inherit maternal chromosomes via premeiotic endomitosis.[19] While genetically identical to the mother, rare recombination in some species introduces limited diversity.[18] In plants and fungi, vegetative propagation utilizes somatic cells or structures like runners, bulbs, tubers, or rhizomes to generate new individuals without seeds; for example, strawberry plants extend stolons that root at nodes, forming independent clones.[20] Spore formation complements this in non-seed plants and fungi, where haploid or diploid spores disperse and germinate mitotically into gametophytes or sporophytes, as in ferns (producing up to millions of spores per frond) and mushrooms.[21] These mechanisms bypass meiosis and fertilization, ensuring rapid colonization in stable environments but limiting adaptability to mutations alone.[18]Distribution and Examples Across Taxa
Asexual reproduction is the predominant mode in prokaryotes, encompassing bacteria and archaea, which replicate via binary fission to produce genetically identical offspring. This process involves DNA replication followed by cell division, allowing for exponential population increases, as observed in model organisms like Escherichia coli.[22][19] In eukaryotic protists, asexual reproduction occurs through mechanisms such as binary fission in amoebae (Amoeba proteus) and multiple fission in ciliates like Paramecium.[23] Fungi commonly utilize asexual spore production or budding; for example, yeasts in the phylum Ascomycota, such as Saccharomyces cerevisiae, bud to form daughter cells, facilitating rapid colonization in nutrient-rich environments.[23][24] Plants exhibit diverse asexual strategies, including vegetative propagation through structures like rhizomes, tubers, and runners, as in potatoes (Solanum tuberosum) via tubers or strawberries (Fragaria × ananassa) via stolons. Apomixis, where seeds form without fertilization, is documented in approximately 2-3% of angiosperm species, enabling clonal seed production in genera like Taraxacum (dandelions).[23] Among animals, asexual reproduction prevails in simpler invertebrates: sponges (phylum Porifera) regenerate via gemmules or budding, while cnidarians such as Hydra propagate by budding, producing genetically identical polyps.[25][26] Parthenogenesis, development from unfertilized eggs, occurs in arthropods like aphids (Aphididae) during population booms and in reptiles such as New Mexico whiptail lizards (Aspidoscelis neomexicana), which are all-female clones.[26] In vertebrates, it remains exceptional and often facultative, as in certain sharks (Carcharhinus species) or the Caucasian rock lizard (Darevskia rudis), but sexual reproduction dominates higher taxa due to genetic recombination benefits.[19] Overall, asexual modes are phylogenetically widespread yet diminish in prevalence with increasing organismal complexity, appearing sporadically in metazoans.[27]Empirical Advantages and Limitations
Asexual reproduction enables rapid proliferation in resource-abundant environments, allowing organisms to capitalize on transient opportunities without delays from mate acquisition. In aphids (Aphididae), parthenogenetic females can produce up to 100 offspring over multiple generations annually, driving explosive population increases during favorable seasons and enabling swift colonization of new habitats.[28] This efficiency stems from direct transmission of the parental genome, bypassing meiosis and recombination costs, which conserves energy for somatic growth and reproduction. Empirical models of bacterial fission, such as Escherichia coli doubling every 20-30 minutes in nutrient-rich media, illustrate how asexual modes support exponential growth rates exceeding those of sexual counterparts under similar conditions.[29] In certain metazoans, asexual budding or fragmentation sustains local dominance where dispersal is limited. For example, in the syllid polychaete Paralvinella misakiensis, budding reproduction yields clonal colonies that persist without evident fitness decline over observed generations, challenging assumptions of inherent long-term inferiority in controlled settings.[30] Such mechanisms reduce vulnerability to mate scarcity, particularly in isolated or high-density populations, and empirical data from fungal spores and plant runners (e.g., strawberries via stolons) confirm higher per capita reproductive output compared to seed-based sexual propagation in stable habitats.[31] Despite these efficiencies, asexual reproduction's empirical limitations arise primarily from constrained genetic variation, rendering populations susceptible to uniform selective pressures. Clonal offspring inherit identical genotypes, limiting adaptive potential against pathogens or climatic shifts; field studies on parthenogenetic lizards (Aspidoscelis spp.) reveal higher parasite loads and localized extinctions when environments fluctuate, as opposed to sexually reproducing congeners with heterozygous advantages.[32] This uniformity facilitates rapid coevolutionary arms races, where antagonists exploit shared vulnerabilities, as evidenced by experimental infections in asexual yeast strains showing faster mutation fixation than sexual analogs.[33] A key constraint is Muller's ratchet, where deleterious mutations accumulate irreversibly in asexual lineages due to the absence of recombination for purging. Simulations and genomic analyses of asexual populations, such as RNA viruses and experimental Saccharomyces cerevisiae lines, demonstrate stepwise declines in fitness as rare beneficial mutations cannot offset linked harmful ones, with ratchet clicks occurring at rates proportional to genome size and mutation load.[34] Empirical evidence from bdelloid rotifers, presumed ancient asexuals, indicates polyploidy or cryptic gene exchange may mitigate this, yet most metazoan asexual clades exhibit elevated mutation burdens and shorter phylogenetic persistence, with meta-analyses estimating asexual species durations 10-100 times briefer than sexual ones across taxa.[31][35] These patterns underscore how, while advantageous short-term, asexual reproduction's genetic bottlenecks constrain evolutionary longevity in dynamic ecosystems.Sexual Reproduction
Anisogamy and the Origins of Sexual Dimorphism
Anisogamy denotes the dimorphic production of gametes differing markedly in size and function, with female gametes (eggs) substantially larger, provisioned with cytoplasm and nutrients for zygote development, and male gametes (spermatozoa) smaller, numerous, and adapted for motility to locate and penetrate eggs.[36] [37] This pattern prevails across sexually reproducing multicellular eukaryotes, including animals, plants, and many algae, where gametic asymmetry defines the male and female sexes.[38] In contrast, isogamy involves gametes of uniform size, as observed in basal lineages like certain fungi and green algae, representing the ancestral state prior to anisogamy's emergence.[39] The evolutionary transition from isogamy to anisogamy arose through disruptive selection on gamete size in ancestral populations. Mathematical models indicate that, under conditions of limited gametic resources and fertilization inefficiency, intermediate-sized gametes yield lower zygote production rates compared to extremes: small gametes, which allow production of vast numbers to enhance fertilization probability via competition, or large gametes, which bolster offspring survival through superior provisioning.[40] [41] Geoffrey A. Parker, Robin Baker, and V. G. Smith formalized this in 1972, demonstrating via game-theoretic analysis that anisogamy evolves as an evolutionarily stable strategy when gamete fusion requires proximity and rarity limits encounters.[40] Empirical support derives from volvocine algae, where gamete dimorphism correlates with organismal complexity and group spawning dynamics, and comparative studies across taxa affirm the model's predictions on female-to-male gamete size ratios exceeding 10:1 in most species.[39] [42] Anisogamy's gametic asymmetry extends to organismal sexual dimorphism by imposing differential reproductive costs and opportunities. The sex investing more per gamete (females) faces higher per-offspring costs, constraining mating rates and favoring mate choice and parental care, while the low-investment sex (males) achieves higher potential reproductive rates, fostering intrasexual competition and greater variance in reproductive success.[37] This causal link, rooted in Bateman's 1948 Drosophila experiments revealing steeper male fitness gains from multiple matings, underpins Robert Trivers' 1972 parental investment theory, explaining ubiquitous dimorphisms such as male-biased size in ornaments, weaponry, and behavioral polygyny across vertebrates and invertebrates.[37] [43] Disruptions, like in species with sex-role reversal (e.g., pipefish), align with inverted investment patterns, underscoring anisogamy's foundational role in dimorphism's origins rather than mere correlation.[44]Gametogenesis and Fertilization Processes
Gametogenesis encompasses the cellular processes by which diploid germ cells undergo meiosis to produce haploid gametes in sexually reproducing eukaryotes. In anisogamous organisms, this yields dimorphic gametes: motile, compact spermatozoa through spermatogenesis in males and immotile, cytoplasm-rich oocytes through oogenesis in females, reflecting adaptations for mobility and provisioning, respectively.[45][46] Spermatogenesis occurs within the testes' seminiferous tubules, initiating from primordial germ cells that differentiate into type A spermatogonia, which proliferate mitotically; some commit to meiosis as primary spermatocytes, undergoing DNA replication and two meiotic divisions to yield four haploid spermatids per primary spermatocyte. Spermiogenesis then remodels spermatids into streamlined spermatozoa, featuring an acrosome, flagellum, and condensed nucleus, with the process recurring continuously from puberty onward in mammals, producing millions of sperm daily.[47] Oogenesis, conversely, transpires in ovarian follicles and begins prenatally in mammals, with oogonia multiplying mitotically before entering prophase I of meiosis to form primary oocytes, which arrest until puberty. Ovulation triggers completion of meiosis I, asymmetrically partitioning cytoplasm to yield a secondary oocyte and a diminutive first polar body; meiosis II arrests again until fertilization, then produces one ovum retaining most cytoplasm and a second polar body, discarding non-functional cells to concentrate resources in the viable gamete. This yields far fewer oocytes—typically 400–500 ovulated over a female's reproductive lifespan—compared to spermatogenesis.[45][46] Fertilization, synonymous with syngamy, fuses a sperm pronucleus with the egg pronucleus to form a diploid zygote, triggering embryonic development while preventing polyspermy via fast (membrane depolarization) and slow (cortical granule exocytosis) blocks. In animals, it commences with sperm-egg recognition, acrosome reaction for zona pellucida penetration, gamete membrane fusion, and calcium-mediated egg activation, which resumes meiosis II and initiates zygotic gene expression; this restores ploidy, combines parental genomes, and leverages the oocyte's provisions for cleavage.[48][49][50]Outcrossing (Allogamy) vs. Self-Fertilization (Autogamy)
Outcrossing, also known as allogamy, refers to the transfer and fusion of gametes between genetically distinct individuals of the same species, which maintains heterozygosity and generates novel genetic combinations through recombination.[51] Self-fertilization, or autogamy, by contrast, involves the union of male and female gametes produced by the same individual, typically in hermaphroditic organisms, resulting in offspring that are genetically identical to the parent except for mutational effects.[52] These mating strategies represent endpoints on a continuum of breeding systems, with many species exhibiting mixed mating where both occur at varying rates depending on ecological pressures such as pollinator availability or population density.[53] Self-fertilization confers a transmission advantage, as a selfing individual passes copies of both its genomes to progeny via seeds, effectively doubling the genetic contribution compared to outcrossing where only one genome is transmitted per gamete.[54] This can yield a twofold numerical superiority in reproductive output under conditions of mate scarcity, bypassing the need for mate location or inter-individual competition for fertilization.[55] However, repeated selfing rapidly increases homozygosity, exposing recessive deleterious alleles and causing inbreeding depression—reduced fitness in offspring manifested as lower survival, fertility, or growth rates.[56] Studies in plants demonstrate that selfed progeny often suffer 20-50% fitness declines initially, though successive generations can purge these mutations, stabilizing selfing lineages at lower but viable fitness levels.[57] Outcrossing counters inbreeding depression by restoring heterozygosity, enhancing adaptability to pathogens, parasites, and fluctuating environments through increased additive genetic variance.[58] Empirical evidence from mutation accumulation experiments shows outcrossers accumulate fewer deleterious mutations over time, as recombination breaks linkage disequilibria and facilitates selection against mutation loads.[55] Drawbacks include energetic costs for mate attraction structures (e.g., elaborate flowers or pheromones) and risks of pollen discounting, where self-pollen interferes with outcross pollen on stigmas.[59] In predominantly selfing populations, low outcrossing rates persist if inbreeding depression exceeds 50%, favoring mechanisms like late-acting self-incompatibility that enforce outcrossing until viable mates are scarce.[60]| Aspect | Outcrossing (Allogamy) | Self-Fertilization (Autogamy) |
|---|---|---|
| Genetic Variation | High; promotes recombination and heterozygosity | Low; leads to homozygosity and clonal-like offspring |
| Fitness Costs/Benefits | Mitigates inbreeding depression; higher adaptability but mate-search overhead | Twofold transmission gain; rapid reproduction but initial inbreeding depression |
| Evolutionary Stability | Maintained by mutation load and pathogen pressure | Evolves repeatedly from outcrossers; limited by purging limits and reversion barriers |
| Empirical Examples | Predominant in animal-pollinated plants; e.g., wild blueberries reliant on cross-pollination for 90%+ seed set | Frequent in colonizing plants; e.g., Epipactis orchids transitioning to autogamy for speciation |
Comparative Dynamics
Trade-offs Between Asexual and Sexual Modes
Asexual reproduction confers a demographic advantage through rapid population growth, as every individual can produce offspring without the need for mating, potentially doubling the reproductive output compared to sexual systems where males contribute no direct progeny.[65] This "two-fold cost of sex," formalized by John Maynard Smith in 1971, arises because sexual females allocate resources to sons that do not bear offspring, whereas asexual lineages invest fully in daughters, enabling faster colonization of favorable environments.[66] Empirical studies in systems like the facultatively sexual snail Potamopyrgus antipodarum confirm that asexual clones initially outperform sexuals in low-parasite habitats due to this efficiency.[67] However, asexual lineages suffer from reduced genetic diversity, limiting adaptability to changing conditions; offspring are genetically identical to the parent (barring mutations), increasing vulnerability to uniform selective pressures such as novel pathogens.[68] Muller's ratchet exacerbates this by causing irreversible accumulation of deleterious mutations in finite populations lacking recombination to purge them, as demonstrated in asexual Caenorhabditis nematodes where mutation loads rise over generations without gene flow.[69] In contrast, sexual reproduction's meiosis and outcrossing generate novel allelic combinations, enhancing long-term fitness by masking recessive deleterious alleles and facilitating adaptation, though at the expense of meiosis's energy demands and mate-search risks.[70] The Red Queen hypothesis posits that coevolving antagonists like parasites favor sex by favoring rare genotypes, providing a counterbalance to asexual proliferation; field data from New Zealand snails show sexuals persisting in high-parasite lakes where asexuals decline due to host-specific adaptations by trematodes.[71] Thus, while asexual modes excel in stable, resource-rich niches—evident in bacterial dominance or parthenogenetic lizards—sexual modes predominate in dynamic ecosystems, trading immediate fecundity for resilient variation.[72]| Trade-off Aspect | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| Reproductive Efficiency | All individuals reproduce; up to 2x faster growth in ideal conditions.[65] | Half the population (males) non-reproductive; slower net output.[66] |
| Genetic Variation | Clonal; low adaptability to change.[68] | High via recombination; better response to selection.[70] |
| Mutation Management | Prone to ratchet; deleterious load accumulates.[69] | Purging via segregation; maintains fitness.[67] |
| Parasite/Environmental Resistance | Vulnerable to coevolving threats; rare long-term persistence.[71] | Diversity confers edge under Red Queen dynamics.[72] |
Evolutionary Persistence Despite Costs
Sexual reproduction imposes a twofold cost compared to asexual reproduction, as only females in sexual populations directly produce offspring, whereas an asexual female can transmit her entire genome to all progeny without allocating resources to non-reproducing males.[73] This cost, combined with expenses for mate location and courtship, predicts that asexual lineages should outcompete sexual ones over time, yet sexual reproduction predominates in most multicellular eukaryotes.[74] Empirical studies in natural systems, such as cyclical parthenogens like the waterflea Daphnia pulex, confirm this cost manifests as reduced asexual frequencies aligning with twofold fitness disadvantages during favorable conditions.[73] The persistence of sex arises primarily from benefits of genetic recombination and outcrossing that counteract these costs in dynamic environments. Recombination generates novel genotypic combinations, enhancing adaptability to fluctuating selection pressures, such as abiotic changes or biotic antagonists, where clonal uniformity in asexuals leads to vulnerability.[75] For instance, models demonstrate that even when sexual fitness is half that of asexual due to the twofold cost, variability from sex maintains evolutionary stability by purging deleterious alleles and fostering resistance to stochastic environmental shifts.[75] A key mechanism is the Red Queen hypothesis, positing that coevolutionary arms races with parasites favor sexuals, as diverse progeny evade host-specific pathogens more effectively than uniform asexual clones.[76] Field experiments with Potamopyrgus antipodarum snails show higher parasitism in asexual genotypes versus sexuals, supporting that parasite-mediated selection sustains sex by imposing negative frequency-dependent fitness on common clones.[76] Similarly, DNA repair during meiosis addresses double-strand breaks and other damage accumulated in germlines, reducing mutation loads that accumulate irreversibly in asexuals via processes like Muller's ratchet, though recombination's masking of recessive lethals provides an additional safeguard.[77] These advantages manifest conditionally: sex thrives under high biotic pressures or mutation rates but may yield to parthenogenesis in stable niches, explaining coexistence in facultative systems.[78] Theoretical analyses indicate recombination's efficacy scales with genome-wide mutation rates exceeding ~1 per haploid genome, sufficient to offset costs by accelerating adaptation and deleterious allele removal.[79] Overall, empirical and modeling evidence underscores that sex's persistence reflects superior long-term evolvability against irreducible sources of environmental and genomic variance, rather than raw reproductive rate.[80]Reproductive Strategies
r-Selection vs. K-Selection Frameworks
The r/K selection framework categorizes reproductive strategies along a continuum based on environmental pressures, where "r" refers to the intrinsic rate of population increase favored in uncrowded or unstable habitats, and "K" denotes carrying capacity efficiency in dense, competitive settings. Originally derived from the logistic growth model by MacArthur and Wilson in 1967, the theory was expanded by Pianka in 1970 to encompass life-history traits, predicting that selection in variable environments promotes rapid colonization through high reproductive output, while stable environments select for sustained viability through resource-efficient reproduction.[81] r-selected strategies prioritize fecundity over offspring quality, characteristic of species in ephemeral or predator-rich niches. These organisms produce large numbers of small gametes or offspring, often via external fertilization or broadcast spawning, with negligible parental investment, short maturation times, and semelparous or highly iteroparous cycles to exploit transient opportunities. Insects like drosophila and many planktonic species exemplify this, releasing thousands to millions of eggs per reproductive event, where high juvenile mortality offsets low per-offspring success.[81]/45:_Population_and_Community_Ecology/45.03:_Life_History_Patterns/45.3B:_Theories_of_Life_History) Conversely, K-selected strategies emphasize quality and survival, suited to predictable environments with density-dependent constraints. Traits include fewer, larger offspring, internal development, viviparity or extensive post-natal care, delayed reproduction, and iteroparity with prolonged lifespans to compete effectively. Large mammals such as wolves (Canis lupus), which invest in pack hunting, territorial defense, and cooperative pup-rearing, produce litters of 4-6 after a 63-day gestation, with survival rates bolstered by familial provisioning.[81][82] Key reproductive differences are summarized in the following correlates adapted from Pianka:| Feature | r-Selection | K-Selection |
|---|---|---|
| Fecundity | High | Low |
| Offspring size | Small | Large |
| Parental care | Absent or minimal | Pronounced |
| Reproductive age | Early | Late |
| Lifespan | Short | Long |