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The evolution of fetal nutritional adaptations
Abstract
Viviparous (live-bearing) vertebrates have evolved a variety of specializations by which the nutritional needs of their embryos can be satisfied. The enormous diversity of these adaptations has been well documented in reviews of fish (Amoroso, 1960; Hoard, 1969; Wourms, 1981), amphibians (Wake, 1977, 1980, 1982), reptiles (Weekes, 1935; Bauchot, 1965), and mammals (Mossman, 1937; Wimsatt, 1962; Luckett, 1977). This paper is a preliminary attempt to examine these adaptations from an evolutionary standpoint. We shall summarize evidence that strong evolutionary convergence in fetal nutritional adaptations has occurred frequently in viviparous vertebrates. Hypothetical explanations for the observed trends are also suggested.
... Matrotrophy and, in particular, placentotrophy are generally regarded as having evolved many times in different classes of vertebrates (Wourms 1981 ;Blackburn et al. 1985 ;Blackburn 1992Blackburn , 1999bBlackburn , 2005aWooding and Burton 2008 ). Similarly, the distribution of the patterns of sexual reproduction across Bryozoa strongly suggests that placentotrophy evolved independently in all three bryozoan classes and within both gymnolaemate orders (Ostrovsky et al. 2009a ). ...
... While modes of EEN have been thoroughly reviewed in vertebrates (Wourms 1981 ;Wourms et al. 1988 ;Wourms and Lombardi 1992 ;Blackburn 1992Blackburn , 1999bBlackburn , 2005bBlackburn et al. 1985 ;Wooding and Burton 2008 ), there has been no attempt to review the topic in invertebrates. Modes of matrotrophy occurring during embryonic incubation include oophagy, adelphophagy, histotrophy, histophagy, and placento trophy (modifi ed from Wourms 1981 andBlackburn et al. 1985 ;Blackburn 1999b ). ...
... While modes of EEN have been thoroughly reviewed in vertebrates (Wourms 1981 ;Wourms et al. 1988 ;Wourms and Lombardi 1992 ;Blackburn 1992Blackburn , 1999bBlackburn , 2005bBlackburn et al. 1985 ;Wooding and Burton 2008 ), there has been no attempt to review the topic in invertebrates. Modes of matrotrophy occurring during embryonic incubation include oophagy, adelphophagy, histotrophy, histophagy, and placento trophy (modifi ed from Wourms 1981 andBlackburn et al. 1985 ;Blackburn 1999b ). Chordates possess all these modes, with placentotrophy commonest. ...
This chapter contains an analysis of the main directions in the evolution of sexual reproduction in bryozoans – changes in modes of oogenesis and fertilization, the transition from plank-totrophy to a non-feeding larva and its consequences, the origin of embryo incubation, and the repeated evolution of matrotrophy and placental analogues. The trends that emerge from this analysis are compared with reproductive analogues in the evolution of the bryozoan order Ctenostomata as well as other marine invertebrate groups (predominantly echino-derms, molluscs and polychaetes). The conditions under which the cheilostomes radiated in the Late Cretaceous are considered in detail, and the consequences of the transitions to new reproductive patterns are analyzed. It is suggested that a shift in oogenesis (reduction in egg number and increase in their size) and parental care can apparently evolve in Cheilostomata sequentially, with a short time lag: oogenesis becomes modifi ed fi rst, with the decrease in the number of offspring compensated soon after by the origin of brooding. Finally, the stages in the evolution of sexual reproduction in other bryozoan groups (classes Phylactolaemata and Stenolaemata) are reconstructed. Keywords Brooding • Evolution • Fertilization • Lecithotrophy • Oogenesis • Placentotrophy • Planktotrophy
... We distinguish five matrotrophic modes ('patterns of matrotrophy' in Blackburn, 2014): (i) oophagy, ingestion of sibling ova or products of their resorption; (ii) embryophagy (=adelphophagy), sibling cannibalism; (iii) histotrophy, absorption (and sometimes phagocytosis, see Section IV.5) of nutrients directly from the surrounding fluid of the parental body cavity, incubation chamber or tissues by the offspring external cell layer; (iv) histophagy, ingestion of secretions from parental tissues or glands, feeding on floating cells and cell debris, or eating maternal tissues or organs, most often epithelium (sometimes hypertrophied) of parental sexual ducts, skin or brood chamber, but also the entire uterus, fat body, intestine, etc. (this last variant is termed 'matrophagy', and considered as a separate mode by Blackburn, 2014); and (v) placentotrophy, EEN involving any form of placenta, defined as 'any intimate apposition or fusion of the fetal organs to the maternal tissues for physiological exchange' (Mossman, 1937, p. 156; see also Wourms, 1981;Blackburn, Evans & Vitt, 1985;Blackburn, 1992Blackburn, , 1999aBlackburn, , 2000Blackburn, , 2014. Schindler & de Vries (1988) described ovarian matrotrophy in teleost fishes as aplacental, despite the apposition of embryonic and ovarian epithelia (but lacking specialized nutritional structures). ...
... Based on Pincheira-Donoso et al. (2013) there are 9193 squamate species; about 1800 species may thus be matrotrophic. Morphological and experimental evidence on placentation has been recorded for species in 13 squamate families (Weekes, 1935;Bauchot, 1965;Blackburn, Vitt & Beuchat, 1984;Blackburn, 1985Blackburn, , 1993Blackburn, , 1994bBlackburn, , 1998Blackburn, , 1999bBlackburn, , 2005Blackburn, , 2014Blackburn et al., 1985;Blüm, 1986;Stewart & Blackburn, 1988;Stewart, 1992Stewart, , 1993Stewart, , 2013Lombardi, 1998;Stewart & Thompson, 1998Thompson, Stewart & Speake, 2000;Blackburn & Vitt, 2002;Jerez & Ramírez-Pinilla, 2003;Villagrán et al., 2005;Ramírez-Pinilla, 2006;Thompson & Speake, 2006;Vieira, de Perez & Ramírez-Pinilla, 2007;Leal & Ramírez-Pinilla, 2008;Blackburn & Flemming, 2009;Stewart & Ecay, 2010, and references therein). Among these, substantial placentotrophy evolved in all six subclades of a single lizard family, Scincidae (Blackburn, 2014). ...
... Matrotrophic patterns encompass numerous structural and physiological variants. These variants reflect stages (often transitional) in the evolution of parental care and apparent trends in the transformation of parent-offspring cell-tissue relationships, studied most thoroughly in vertebrates (reviewed in Blackburn et al., 1985;Blackburn, 1992Blackburn, , 1999bBlackburn, , 2014Wake, 1992;Wourms & Lombardi, 1992;Wooding & Burton, 2008;Hemberger, 2013). Recently Blackburn (2014, p. 20) highlighted the morphological and evolutionary principles that, together with the selective background, shape the evolutionary trajectories of matrotrophy in vertebrates. ...
... We distinguish five matrotrophic modes ('patterns of matrotrophy' in Blackburn, 2014): (i) oophagy, ingestion of sibling ova or products of their resorption; (ii) embryophagy (=adelphophagy), sibling cannibalism; (iii) histotrophy, absorption (and sometimes phagocytosis, see Section IV.5) of nutrients directly from the surrounding fluid of the parental body cavity, incubation chamber or tissues by the offspring external cell layer; (iv) histophagy, ingestion of secretions from parental tissues or glands, feeding on floating cells and cell debris, or eating maternal tissues or organs, most often epithelium (sometimes hypertrophied) of parental sexual ducts, skin or brood chamber, but also the entire uterus, fat body, intestine, etc. (this last variant is termed 'matrophagy', and considered as a separate mode by Blackburn, 2014); and (v) placentotrophy, EEN involving any form of placenta, defined as 'any intimate apposition or fusion of the fetal organs to the maternal tissues for physiological exchange' (Mossman, 1937, p. 156; see also Wourms, 1981;Blackburn, Evans & Vitt, 1985;Blackburn, 1992Blackburn, , 1999aBlackburn, , 2000Blackburn, , 2014. Schindler & de Vries (1988) described ovarian matrotrophy in teleost fishes as aplacental, despite the apposition of embryonic and ovarian epithelia (but lacking specialized nutritional structures). ...
... Based on Pincheira-Donoso et al. (2013) there are 9193 squamate species; about 1800 species may thus be matrotrophic. Morphological and experimental evidence on placentation has been recorded for species in 13 squamate families (Weekes, 1935;Bauchot, 1965;Blackburn, Vitt & Beuchat, 1984;Blackburn, 1985Blackburn, , 1993Blackburn, , 1994bBlackburn, , 1998Blackburn, , 1999bBlackburn, , 2005Blackburn, , 2014Blackburn et al., 1985;Blüm, 1986;Stewart & Blackburn, 1988;Stewart, 1992Stewart, , 1993Stewart, , 2013Lombardi, 1998;Stewart & Thompson, 1998Thompson, Stewart & Speake, 2000;Blackburn & Vitt, 2002;Jerez & Ramírez-Pinilla, 2003;Villagrán et al., 2005;Ramírez-Pinilla, 2006;Thompson & Speake, 2006;Vieira, de Perez & Ramírez-Pinilla, 2007;Leal & Ramírez-Pinilla, 2008;Blackburn & Flemming, 2009;Stewart & Ecay, 2010, and references therein). Among these, substantial placentotrophy evolved in all six subclades of a single lizard family, Scincidae (Blackburn, 2014). ...
... Matrotrophic patterns encompass numerous structural and physiological variants. These variants reflect stages (often transitional) in the evolution of parental care and apparent trends in the transformation of parent-offspring cell-tissue relationships, studied most thoroughly in vertebrates (reviewed in Blackburn et al., 1985;Blackburn, 1992Blackburn, , 1999bBlackburn, , 2014Wake, 1992;Wourms & Lombardi, 1992;Wooding & Burton, 2008;Hemberger, 2013). Recently Blackburn (2014, p. 20) highlighted the morphological and evolutionary principles that, together with the selective background, shape the evolutionary trajectories of matrotrophy in vertebrates. ...
Matrotrophy, the continuous extra-vitelline supply of nutrients from the parent to the progeny during gestation, is one of the masterpieces of nature, contributing to offspring fitness and often correlated with evolutionary diversification. The most elaborate form of matrotrophy—placentotrophy—is well known for its broad occurrence among vertebrates, but the comparative distribution and structural diversity of matrotrophic expression among invertebrates is wanting. In the first comprehensive analysis of matrotrophy across the animal kingdom, we report that regardless of the degree of expression, it is established or inferred in at least 21 of 34 animal phyla, significantly exceeding previous accounts and changing the old paradigm that these phenomena are infrequent among invertebrates. In 10 phyla, matrotrophy is represented by only one or a few species, whereas in 11 it is either not uncommon or widespread and even pervasive. Among invertebrate phyla, Platyhelminthes, Arthropoda and Bryozoa dominate, with 162, 83 and 53 partly or wholly
matrotrophic families, respectively. In comparison, Chordata has more than 220 families that include or consist entirely of matrotrophic species. We analysed the distribution of reproductive patterns among and within invertebrate phyla using recently published molecular phylogenies: matrotrophy has seemingly evolved at least 140 times in all major superclades: Parazoa and Eumetazoa, Radiata and Bilateria, Protostomia and Deuterostomia, Lophotrochozoa and Ecdysozoa. In Cycliophora and some Digenea, it may have evolved twice in the same life cycle. The provisioning of developing young is associated with almost all known types of incubation chambers, with matrotrophic viviparity more widespread (20 phyla) than brooding (10 phyla). In nine phyla, both matrotrophic incubation types are present. Matrotrophy is expressed in five nutritivemodes, of which histotrophy and placentotrophy are most prevalent. Oophagy, embryophagy and histophagy are rarer, plausibly evolving through heterochronous development of the embryonic mouthparts and digestive system. During gestation, matrotrophic modes can shift, intergrade, and be performed simultaneously. Invertebrate matrotrophic adaptations are less complex structurally than in chordates, but they are more diverse, being formed either by a parent, embryo, or both. In a broad and still preliminary sense, there are
indications of trends or grades of evolutionarily increasing complexity of nutritive structures: formation of (i) local zones of enhanced nutritional transport (placental analogues), including specialized parent–offspring cell complexes and various appendages increasing the entire secreting and absorbing surfaces as well as the contact surface between embryo and parent, (ii) compartmentalization of the common incubatory space into more compact and ‘isolated’ chambers with presumably more effective nutritional relationships, and (iii) internal secretory (‘milk’) glands. Some placental analogues in onychophorans and arthropods mimic the simplest placental variants in vertebrates, comprising striking examples of convergent evolution acting at all levels—positional, structural and physiological.
... Matrotrophy and, in particular, placentotrophy are generally regarded as having evolved many times in different classes of vertebrates (Wourms 1981 ;Blackburn et al. 1985 ;Blackburn 1992Blackburn , 1999bBlackburn , 2005aWooding and Burton 2008 ). Similarly, the distribution of the patterns of sexual reproduction across Bryozoa strongly suggests that placentotrophy evolved independently in all three bryozoan classes and within both gymnolaemate orders (Ostrovsky et al. 2009a ). ...
... While modes of EEN have been thoroughly reviewed in vertebrates (Wourms 1981 ;Wourms et al. 1988 ;Wourms and Lombardi 1992 ;Blackburn 1992Blackburn , 1999bBlackburn , 2005bBlackburn et al. 1985 ;Wooding and Burton 2008 ), there has been no attempt to review the topic in invertebrates. Modes of matrotrophy occurring during embryonic incubation include oophagy, adelphophagy, histotrophy, histophagy, and placento trophy (modifi ed from Wourms 1981 andBlackburn et al. 1985 ;Blackburn 1999b ). ...
... While modes of EEN have been thoroughly reviewed in vertebrates (Wourms 1981 ;Wourms et al. 1988 ;Wourms and Lombardi 1992 ;Blackburn 1992Blackburn , 1999bBlackburn , 2005bBlackburn et al. 1985 ;Wooding and Burton 2008 ), there has been no attempt to review the topic in invertebrates. Modes of matrotrophy occurring during embryonic incubation include oophagy, adelphophagy, histotrophy, histophagy, and placento trophy (modifi ed from Wourms 1981 andBlackburn et al. 1985 ;Blackburn 1999b ). Chordates possess all these modes, with placentotrophy commonest. ...
Chapter 1 is devoted to reproductive patterns in gymnolaemate bryozoans, especially oogenesis, fertilization and brooding in the order Cheilostomata. Following a brief review of the history of studies on cheilostome reproduction, the cell source, position and development of the gonads, sexual structure of colonies and fertilization are described, followed by a detailed description and comparative analysis of the fi ve major reproductive patterns. Correlations are demonstrated between the type of oogenesis (oligolecithal vs macroleci-thal), ovary structure and type of embryonic incubation (non-placental vs placental). Matrotrophy is far more common in Cheilostomata than previously realized, with placental analogues being associated with the various brood-chamber types. Both incipient and substantial matrotrophy have been recorded. Sexual polymorphism, precocious fertilization, nurse cells, coelomopores and oviposition are described from the literature and new data and their evolution is discussed.
... The increased and prolonged maternal provisioning during embryonic development takes place in several animal groups through the placenta or placenta-like structures (Blackburn et al. 1985). This probably evolved from preexisting tissues that acquired new functional attributes, modified their developmental programs, and evolved novel cell types (Griffith and Wagner 2017), allowing a close association between mother and offspring tissues, and an efficient exchange of nutrients, gases and excretions (Mossman 1991; Wooding and Burton 2008). ...
Viviparity has evolved from oviparity approximately 142 times among vertebrates. Different theories have been proposed to explain the evolution of each of its traits in the different taxa. None, however, is applicable to all the viviparous vertebrates, since the derived ecological advantages such as controlling incubating temperature or protecting eggs against predation differ amongst clades. Most theories have been developed under a co-adaptive perspective, whereas less attention has been paid to conflict. We developed a broad panorama of the gradual evolution, from oviparity to advanced forms of viviparity, that includes the different environmental and co-adaptive selective pressures that have been suggested to be at the root of the different instances of viviparity and of the diverse maternal–foetal adaptations for nutrient transfer seen amongst vertebrates. Furthermore, we highlight the importance of conflict as a crucial driver of the evolution of many of those traits, including the evolution of epigenetic control of maternal resources. We suggest that the different types of matrotrophic viviparity, and probably also some reversals to oviparity, have been the result of an antagonistic coevolution between mothers, fathers and offspring, and their genomes. We additionally suggest that the appearance of a trait that allowed or favoured the evolution of internal development and matrotrophy generates a new selective environment that promotes further adaptations or counteradaptations, leading to the observed diversity of forms of embryonic development, nourishment, and transfer of maternal nutrients, and ultimately to the diversity of extant viviparous taxa.
... According to Mossman ([10], p. 156), a placenta is "any intimate apposition or fusion of the fetal organs to the maternal tissues for physiological exchange". Whereas vertebrate placentae are mostly (although not always) of a similar origin involving sexual ducts and embryonic envelopes (reviewed in [4,6,9,[11][12][13][14]), the placental analogues of invertebrates originated from a plethora of tissues and organs and sometimes involve embryonic envelopes as well. Generally, a 'placental analogue' is any local zone of enhanced nutritional transport developing during incubation, from simple apposition of nonspecialized epithelia to specialized parental-embryonic tissue/cell complexes that increase the entire secreting and absorbing surfaces. ...
Background
Placentation has evolved multiple times among both chordates and invertebrates. Although they are structurally less complex, invertebrate placentae are much more diverse in their origin, development and position. Aquatic colonial suspension-feeders from the phylum Bryozoa acquired placental analogues multiple times, representing an outstanding example of their structural diversity and evolution. Among them, the clade Cyclostomata is the only one in which placentation is associated with viviparity and polyembryony—a unique combination not present in any other invertebrate group.
Results
The histological and ultrastructural study of the sexual polymorphic zooids (gonozooids) in two cyclostome species, Crisia eburnea and Crisiella producta, revealed embryos embedded in a placental analogue (nutritive tissue) with a unique structure—comprising coenocytes and solitary cells—previously unknown in animals. Coenocytes originate via nuclear multiplication and cytoplasmic growth among the cells surrounding the early embryo. This process also affects cells of the membranous sac, which initially serves as a hydrostatic system but later becomes main part of the placenta. The nutritive tissue is both highly dynamic, permanently rearranging its structure, and highly integrated with its coenocytic ‘elements’ being interconnected via cytoplasmic bridges and various cell contacts. This tissue shows evidence of both nutrient synthesis and transport (bidirectional transcytosis), supporting the enclosed multiple progeny. Growing primary embryo produces secondary embryos (via fission) that develop into larvae; both the secondary embyos and larvae show signs of endocytosis. Interzooidal communication pores are occupied by 1‒2 specialized pore-cells probably involved in the transport of nutrients between zooids.
Conclusions
Cyclostome nutritive tissue is currently the only known example of a coenocytic placental analogue, although syncytial ‘elements’ could potentially be formed in them too. Structurally and functionally (but not developmentally) the nutritive tissue can be compared with the syncytial placental analogues of certain invertebrates and chordates. Evolution of the cyclostome placenta, involving transformation of the hydrostatic apparatus (membranous sac) and change of its function to embryonic nourishment, is an example of exaptation that is rather widespread among matrotrophic bryozoans. We speculate that the acquisition of a highly advanced placenta providing massive nourishment might support the evolution of polyembryony in cyclostomes. In turn, massive and continuous embryonic production led to the evolution of enlarged incubating polymorphic gonozooids hosting multiple progeny.
... According to Mossman ([10], p. 156), a placenta is "any intimate apposition or fusion of the fetal organs to the maternal tissues for physiological exchange". Whereas vertebrate placentae are mostly (although not always) of a similar origin involving sexual ducts and embryonic envelopes (reviewed in [4,6,9,[11][12][13][14]), the placental analogues of invertebrates originated from a plethora of tissues and organs and sometimes involve embryonic envelopes as well. Generally, a 'placental analogue' is any local zone of enhanced nutritional transport developing during incubation, from simple apposition of nonspecialized epithelia to specialized parental-embryonic tissue/cell complexes that increase the entire secreting and absorbing surfaces. ...
Background
Placentation has evolved multiple times among both chordates and invertebrates. Although they are structurally less complex, invertebrate placentae are much more diverse in their origin, development and position. Aquatic colonial suspension-feeders from the phylum Bryozoa acquired placental analogues multiple times, representing an outstanding example of their structural diversity and evolution. Among them, the clade Cyclostomata is the only one in which placentation is associated with viviparity and polyembryony—a unique combination not present in any other invertebrate group.
Results
The histological and ultrastructural study of the sexual polymorphic zooids (gonozooids) in two cyclostome species, Crisia eburnea and Crisiella producta , revealed embryos embedded in a placental analogue (nutritive tissue) with a unique structure—comprising coenocytes and solitary cells—previously unknown in animals. Coenocytes originate via nuclear multiplication and cytoplasmic growth among the cells surrounding the early embryo. This process also affects cells of the membranous sac, which initially serves as a hydrostatic system but later becomes main part of the placenta. The nutritive tissue is both highly dynamic, permanently rearranging its structure, and highly integrated with its coenocytic ‘elements’ being interconnected via cytoplasmic bridges and various cell contacts. This tissue shows evidence of both nutrient synthesis and transport (bidirectional transcytosis), supporting the enclosed multiple progeny. Growing primary embryo produces secondary embryos (via fission) that develop into larvae; both the secondary embyos and larvae show signs of endocytosis. Interzooidal communication pores are occupied by 1‒2 specialized pore-cells probably involved in the transport of nutrients between zooids.
Conclusions
Cyclostome nutritive tissue is currently the only known example of a coenocytic placental analogue, although syncytial ‘elements’ could potentially be formed in them too. Structurally and functionally (but not developmentally) the nutritive tissue can be compared with the syncytial placental analogues of certain invertebrates and chordates. Evolution of the cyclostome placenta, involving transformation of the hydrostatic apparatus (membranous sac) and change of its function to embryonic nourishment, is an example of exaptation that is rather widespread among matrotrophic bryozoans. We speculate that the acquisition of a highly advanced placenta providing massive nourishment might support the evolution of polyembryony in cyclostomes. In turn, massive and continuous embryonic production led to the evolution of enlarged incubating polymorphic gonozooids hosting multiple progeny.
The reproductive diversity of extant cartilaginous fishes (class Chondrichthyes) is extraordinarily broad, reflecting more than 400 million years of evolutionary history. Among their many notable reproductive specialisations are viviparity (live‐bearing reproduction) and matrotrophy (maternal provision of nutrients during gestation). However, attempts to understand the evolution of these traits have yielded highly discrepant conclusions. Here, we compile and analyse the current knowledge on the evolution of reproductive diversity in Chondrichthyes with particular foci on the frequency, phylogenetic distribution, and directionality of evolutionary changes in their modes of reproduction. To characterise the evolutionary transformations, we amassed the largest empirical data set of reproductive parameters to date covering nearly 800 extant species and analysed it via a comprehensive molecular‐based phylogeny. Our phylogenetic reconstructions indicated that the ancestral pattern for Chondrichthyes is ‘short single oviparity’ (as found in extant holocephalans) in which females lay successive clutches (broods) of one or two eggs. Viviparity has originated at least 12 times, with 10 origins among sharks, one in batoids, and (based on published evidence) another potential origin in a fossil holocephalan. Substantial matrotrophy has evolved at least six times, including one origin of placentotrophy, three separate origins of oophagy (egg ingestion), and two origins of histotrophy (uptake of uterine secretions). In two clades, placentation was replaced by histotrophy. Unlike past reconstructions, our analysis reveals no evidence that viviparity has ever reverted to oviparity in this group. Both viviparity and matrotrophy have arisen by a variety of evolutionary sequences. In addition, the ancestral pattern of oviparity has given rise to three distinct egg‐laying patterns that increased clutch (brood) size and/or involved deposition of eggs at advanced stages of development. Geologically, the ancestral oviparous pattern arose in the Paleozoic. Most origins of viviparity and matrotrophy date to the Mesozoic, while a few that are represented at low taxonomic levels are of Cenozoic origin. Coupled with other recent work, this review points the way towards an emerging consensus on reproductive evolution in chondrichthyans while offering a basis for future functional and evolutionary analyses. This review also contributes to conservation efforts by highlighting taxa whose reproductive specialisations reflect distinctive evolutionary trajectories and that deserve special protection and further investigation.
Amphibians and reptiles are a diverse group of ectothermic vertebrates that occupy a variety of habitats in rangelands of North America, from wetlands to the driest deserts. These two classes of vertebrates are often referred to as herpetofauna and are studied under the field of herpetology. In U.S. rangelands, there are approximately 66 species of frogs and toads, 58 salamanders, 98 lizards, 111 snakes, and 27 turtles and tortoises. Herpetofauna tend to be poorly studied compared with other vertebrates, which creates a challenge for biologists and landowners who are trying to manage rangeland activities for this diverse group of animals and their habitats. Degradation of habitats from human land use and alteration of natural processes, like wildfire, are primary threats to herpetofauna populations. Disease, non-native predators, collection for the pet trade, and persecution are also conservation concerns for some species. Properly managed livestock grazing is generally compatible with herpetofauna conservation, and private and public rangelands provide crucial habitat for many species. Climate change also poses a threat to herpetofauna, but we have an incomplete understanding of the potential effects on species. Dispersal and adaptation could provide some capacity for species to persist on rangelands as climates, disturbance regimes, and habitats change. However, inadequate information and considerable uncertainty will make climate mitigation planning difficult for the foreseeable future. Planning for and mitigating effects of climate change, and interactions with other stressors, is an urgent area for research. Maintaining large, heterogeneous land areas as rangelands will certainly be an important part of the conservation strategy for herpetofauna in North America.
Simple Summary
The diversity of reproductive mechanism in bony fishes is greater than in any other group of vertebrates. It ranges from oviparous, to several stages of viviparous forms. In this context, scorpaenoid fishes belonging to the families Scorpaenidae and Sebastidae are of particular interest, since they show extremely varied reproductive modes connected with ovarian structures. We describe here the ovarian morphology of five rockfish species showing different reproductive modalities, using histology. Specialized microscopic features were found during gametogenesis, strictly related to the production of gelatinous mass surrounding the eggs, typical of these species. Based on microscopic maturity stages here analyzed, we found that all species shed eggs more than once through the spawning season, and were characterized by continuous oogenesis with multiple oocyte deposition. Further ovarian dynamic observations supported the hypothesis that all species had an indeterminate fecundity.
Abstract
The sub-order Scorpenoidei appears to be particularly interesting due to the presence of intermediate stages between oviparity and viviparity in several species. The present study aims to describe the ovarian morphology, using a histological and histochemical approach, in four ovuliparous species belonging to Scorpaena genus compared with a zygoparous species, H. dactylopterus, focusing also on the assessment of the ovarian dynamics in the populations of such species in Sardinia waters (central–western Mediterranean). Ovarian sections of all species were examined using light microscopy. All species showed a specialized ovary, cystovarian type II-3, strictly related to the production of gelatinous matrices surrounding the eggs. Some microscopic peculiarities in the oogenesis process were found: thin zona pellucida, small and low cortical alveoli, and a specialized ovarian wall during the spawning period. All species analyzed were batch-spawners with an asynchronous ovarian organization. A continuous recruitment of oocytes and the occurrence of de novo vitellogenesis was also observed. During the spawning period, low atresia intensity was detected, while a marked increase in this intensity found in the ovaries at the end of spawning season. Our observations may support an indeterminate fecundity type for these species.
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