THE NACREOUS WALLS OF SIEVE ELEMENTS IN SEAGRASSES

The nacreous walls of sieve elements occur in seagrasses in all three genera of the family Zosteraceae and the genus Halodule of the family Cymodoceaceae but are absent from another eight seagrass genera belonging to the families Hydrocharitaceae, Cymodoceaceae, and Posidoniaceae. They occur in leaf blades, leaf sheaths, rhizomes, and erect stems but are not present in root tissues. The nacreous wall is uneven along the inner limits reflecting irregular thickness. The wall consists of hemicellulose or pectin and cellulose, but no protein, lignin, or lipid. Ultrastructurally, the wall contains parallel microfibrils or loose fibrils embedded in an amorphous matrix. Open pores occur in sieve plates and branching plasmodesmata are present in enlarged sieve areas. Mitochondria, endoplasmic reticulum, and plastids are also present in these sieve elements.     

Parallel floral adaptations to pollination by fungus gnats within the genus Mitella (Saxifragaceae)

The widespread pattern of parallel flower evolution as an adaptation for particular pollinator agents, known as "pollination syndromes", has long drawn attention from evolutionary biologists. Here, we report parallel evolution of saucer-shaped flowers and an associated unusual pollination system within the lineage Heucherina, a group of saxifragaceous genera. Field observations reveal that 18 of 28 plant species studied are pollinated almost exclusively by fungus gnats (Mycetophilidae). Among the 18 species with a fungus-gnat pollination system, 13 have characteristic saucer-shaped flowers and are pollinated mainly by several unspecialized mycetophilid genera with short mouthparts. We performed phylogenetic analyses using nucleotide sequences of external and internal transcribed spacers of nuclear ribosomal DNA and reconstructed ancestral floral morphologies with an establishment of the model of floral character evolution under a maximum-likelihood framework. Our analysis indicates that there is significant directionality in the evolutionary shifts of floral forms in the Heucherina. The inferred phylogeny further supports four origins of saucer-shaped flowers, which is shared among 14 species that are traditionally classified into the genus Mitella. In addition, our analysis indicates the extensive polyphyly of genus Mitella, as also suggested previously. The results suggest that the flower-visiting fungus gnats have caused convergent selection for the saucer-shaped flower repeatedly evolved within Heucherina.     

Exine Micromorphology of Orchidinae (Orchidoideae,Orchidaceae): Phylogenetic Constraints or Ecological Influences?

BACKGROUND AND AIMS: Pollen characters have been widely used in defining evolutionary trends in orchids. In recent years, information on pollination biology and phylogenetic patterns within Orchidinae has become available. Hence, the aim of the presented work is to re-evaluate exine micromorphology of Orchidinae in light of recent phylogenetic studies and to test whether pollen micromorphology strictly depends on phylogenetic relationships among species or whether it is influenced by the marked differences in pollination ecology also reported among closely related species. METHODS: Pollen sculpturing of 45 species of Orchidinae and related taxa was investigated using scanning electron microscopy. To cover potential intraspecific variation, several accessions of the same species were examined. KEY RESULTS: Orchidinae show remarkable variation in exine sculpturing, with a different level of variation within species groups. In some genera, such as Serapias (rugulate) and Ophrys (psilate to verrucate), intrageneric uniformity corresponds well to a common pollination strategy and close relationships among species. However, little exine variability (psilate-scabrate and scabrate-rugulate) was also found in the genus Anacamptis in spite of striking differences in floral architecture and pollination strategies. A larger variety of exine conditions was found in genera Dactylorhiza (psilate, psilate-scabrate and reticulate) and Orchis s.s. (psilate, reticulate, perforate-rugulate and baculate) where no unequivocal correspondence can be found to either phylogenetic patterns or pollination strategies. CONCLUSIONS: Changes in pollen characteristics do not consistently reflect shifts in pollination strategy. A unique trend of exine evolution within Orchidinae is difficult to trace. However, the clades comprising Anacamptis, Neotinea, Ophrys and Serapias show psilate to rugulate or scabrate pollen, while that of the clade comprising Chamorchis, Dactylorhiza, Gymnadenia, Orchis s.s., Platanthera, Pseudorchis and Traunsteinera ranges from psilate to reticulate. Comparison of the data with exine micromorphology from members of the tribe Orchidieae and related tribes suggests a possible general trend from reticulate to psilate.     

Phylogeny and radiation of pollination systems in DISA (Orchidaceae)

We studied the patterns of adaptive radiation in Disa, a large orchid genus in southern Africa. A cladogram for 27 species was constructed using 44 morphological characters. Pollination systems were then mapped onto the phylogeny in order to analyze pathways of floral evolution. Shifts from one pollination system to another have been a major feature of the evolutionary diversification of Disa. Unlike many plant genera that are pollinated mainly by a single group of insects, radiation in Disa has encompassed nearly all major groups of pollinating insects; in all, 19 different specialized pollination systems have been found in the 27 species included in this analysis. Another striking pattern is the repeated evolution of broadly similar pollination systems in unrelated clades. For example, butterfly-pollinated flowers have evolved twice; showy deceptive flowers pollinated by carpenter bees, twice; long-spurred flowers pollinated by long-tongued flies, four times; night-scented flowers pollinated by moths, three times; and self-pollination, three times. This suggests that a few dominant pollinator species in a region may be sufficient to generate diversification in plants through repeated floral shifts that never retrace the same pathways.     

EVOLUTION OF PLANT POLLINATION SYSTEMS: HYPOTHESES AND TESTS WITH THE NEOTROPICAL VINE DALECHAMPIA

The results of pollination and mating-system studies were integrated with a phylogenetic study of 40 Neotropical species of Dalechampia L. (Euphorbiaceae) to reconstruct the history of evolutionary change in pollination systems. The results of this analysis were treated as a hypothesis and tested for circularity problems and robustness in the face of changes in the data set. The historical hypothesis was used to make specific predictions about details of pollination ecology and reward biochemistry; the predictions were supported by independent observations. I conclude that pollination systems in Dalechampia have been evolutionarily labile, relative to most morphological features, with repeated parallelisms and reversals. Transitions among the three pollination systems evolved by Dalechampia (pollination by resin-collecting bees, fragrance-collecting male euglossine bees, and pollen-collecting bees) have been facilitated by biochemical exaptation (preadaptation). Pollination by male euglossine bees is relatively rare in the genus but has originated independently three to four times. In contrast, pollination by resin-collecting female bees is very common, but has originated only once. Eighty-six to 97% of transitions between pollination systems involved an intermediate phase during which both old and new pollinators were effective, but 3 to 14% of transitions may have been “instantaneous,” lacking the intermediate phase. Clades of species secreting resin rewards are about 10 times as species rich as clades of species secreting fragrance rewards; circumstantial evidence suggests that different extinction rates may be responsible for this difference. Relatively allogamous (cross-pollinating) species have evolved from more autogamous (self-pollinating) species up to 13 times, and autogamous species have evolved from more allogamous ones up to 11 times. Species occurring in disturbed habitats are facultatively autogamous, whereas species of undisturbed habitats are often highly allogamous.     

Oil-producing flowers within the Iridoideae (Iridaceae): evolutionary trends in the flowers of the New World genera

Background and Aims

Oil-producing flowers related to oil-bee pollination are a major innovation in Neotropical and Mexican Iridaceae. In this study, phylogenetic relationships were investigated among a wide array of New World genera of the tribes Sisyrinchieae, Trimezieae and Tigridieae (Iridaceae: Iridoideae) and the evolution of floral glandular structures, which are predominantly trichomal elaiophores, was examined in relation to the diversification of New World Iridaceae.

Methods

Phylogenetic analyses based on seven molecular markers obtained from 97 species were conducted to produce the first extensive phylogeny of the New World tribes of subfamily Iridoideae. The resulting phylogenetic hypothesis was used to trace the evolutionary history of glandular structures present in the flowers of numerous species in each tribe. Hypotheses of differential diversification rates among lineages were also investigated using both topological and Binary-State Speciation and Extinction methods.

Key Results and Conclusions

Floral glandular structures and especially trichomal elaiophores evolved multiple times independently in the American tribes of Iridoideae. The distribution pattern of species displaying glandular trichomes across the phylogeny reveals lability in the pollination system and suggests that these structures may have played a significant role in the diversification of the Iridoideae on the American continent.     

苦苣苔科镜像花的多样性及演化

泛热带分布的苦苣苔科(Gesneriaceae)在我国南方具有极高的物种丰富度与特有率,花部特征变化丰富,是研究物种形成与适应演化的代表类群。镜像花(mirror-image flowers)是极为特化的传粉系统,在苦苣苔科中出现了较多的不同类型,可能与苦苣苔科物种多样性形成与维持有关。该研究总结与分析了苦苣苔科镜像花的类型多样性以及系统分布与适应演化等,讨论了镜像花对苦苣苔科物种形成与维持的积极意义。结果表明:镜像花仅分布在亚洲和非洲的苦苣苔亚科(Didymocarpoideae)的7个属,在历史上就至少发生了5次独立起源。长冠苣苔属(Rhabdothamnopsis)、南洋苣苔属(Henckelia)及长蒴苣苔属(Didymocarpus)镜像花的花柱与可育雄蕊分别向左、右两侧偏转,形成互补镜像花;蛛毛苣苔属(Paraboea)、喜鹊苣苔属(Ornithoboea)、非洲堇属(Saintpaulia)镜像花缺乏与花柱对应侧偏的可育雄蕊(非互补镜像花);而海角苣苔属(Streptocarpus)直立堇兰亚属(subg.Streptocarpella Engler)则同时出现了互补、非互补镜像花。不同于其他被子植物(离瓣花、缺乏花冠筒),苦苣苔科中的镜像花大多伴随着明显的花冠筒、内藏的雄蕊、合生的花药,以非互补镜像花为主;传粉者以小型的无垫蜂(Amegilla spp.)和熊蜂(Bombus spp.)为主。这些特殊的花部综合征与特化的传粉机制,提高了传粉精确性,可能促进了传粉隔离与物种适应辐射。今后的一个研究重点应通过分子系统发育方法,进一步揭示苦苣苔亚科互补与非互补镜像花的进化顺序及其在物种分化与长距离扩散过程中的可能作用。     

Evolution of a complex coevolved trait: active pollination in a genus of fig wasps

Only three insect lineages have evolved complex active pollination behaviour and only fig wasps (Agaonidae) have also reverted from active to passive pollination. Previously, it was assumed that there was a single origin of active pollination in fig wasps, followed by one independent loss in each of five genera. We show here that there have been three to six changes in pollination behaviour within just one genus (Pleistodontes). The results suggest multiple gains of active pollination in fig wasps, but are sensitive to assumptions about the relative costs of gaining and losing this complex behaviour. In addition, previous comparative studies at higher taxonomic levels have reported correlated evolution between active pollination in wasps and low anther/ovule ratios in figs. We report that changes in pollination behaviour between congeneric species correlate perfectly with changes in anther/ovule ratios in the host figs, showing no phylogenetic inertia in coadaptation at the species level.     

The evolution of bat pollination: a phylogenetic perspective

Background

Most tropical and subtropical plants are biotically pollinated, and insects are the major pollinators. A small but ecologically and economically important group of plants classified in 28 orders, 67 families and about 528 species of angiosperms are pollinated by nectar-feeding bats. From a phylogenetic perspective this is a derived pollination mode involving a relatively large and energetically expensive pollinator. Here its ecological and evolutionary consequences are explored.

Scope and Conclusions

This review summarizes adaptations in bats and plants that facilitate this interaction and discusses the evolution of bat pollination from a plant phylogenetic perspective. Two families of bats contain specialized flower visitors, one in the Old World and one in the New World. Adaptation to pollination by bats has evolved independently many times from a variety of ancestral conditions, including insect-, bird- and non-volant mammal-pollination. Bat pollination predominates in very few families but is relatively common in certain angiosperm subfamilies and tribes. We propose that flower-visiting bats provide two important benefits to plants: they deposit large amounts of pollen and a variety of pollen genotypes on plant stigmas and, compared with many other pollinators, they are long-distance pollen dispersers. Bat pollination tends to occur in plants that occur in low densities and in lineages producing large flowers. In highly fragmented tropical habitats, nectar bats play an important role in maintaining the genetic continuity of plant populations and thus have considerable conservation value.     

Pollination in conifers

Our understanding of pollination in conifers has advanced rapidly in recent years, but it still lags behind our knowledge of this process in angiosperms. In part this is because conifers are not considered to be high priority crops and, unlike many cultivated flowers, conifer seed cones are generally neither large nor colorful. The use of genetics to improve tree growth has primarily been through selection and asexual propagation rather than breeding, and because incompatibility is not thought to occur in conifer pollination systems, concern about pollination has primarily been with regard to seed production. Here we examine the ancestral wind-pollination mechanism in conifers and discuss how the process may have evolved to improve pollination success.     

Sexual mimicry in Mormolyca ringens (Lindl.) Schltr. (Orchidaceae: Maxillariinae)

BACKGROUND AND AIMS: Pollination through sexual mimicry, also known as pseudocopulation, has been suggested to occur in some genera of the Neotropical orchid subtribe Maxillariinae. However, it has been demonstrated so far only for Trigonidium obtusum. This study reports and illustrates pollination through sexual mimicry in Mormolyca ringens. METHODS: A total of 70 h were dedicated to the observation of flowers and pollinator behaviour, which was photographically recorded. Flower features involved in pollinator attraction were studied using a stereomicroscope and by SEM analyses. Preliminary observations on the plant breeding system were made by manually self-pollinating flowers. The chemical composition of the fragrance volatiles was determined by GC/MS analysis. KEY RESULTS: The flower features of M. ringens parallel those of other pseudocopulatory flowers. The labellum shape and indument are reminiscent of an insect. Sexually excited drones of Nannotrigona testaceicornis and Scaptotrigona sp. (both in the Apidae: Meliponini) attempt copulation with the labellum and pollinate the flower in the process. In both bee species, the pollinarium is attached to the scutellum. Pollinator behaviour may promote some degree of self-pollination, but preliminary observations indicate that M. ringens flowers are self-incompatible. Flowers are produced all the year round, which ties in with the production of bee males several times a year. The phylogenetic relationships of M. ringens are discussed and a number of morphological and phenological features supporting them are reported. CONCLUSIONS: It is expected that further research could bring to light whether other Maxillariinae species are also pollinated through sexual mimicry. When a definitive and robust phylogeny of this subtribe is available, it should be possible to determine how many times pseudocopulation evolved and its possible evolutionary history.     

Pollen in the guts of Permian insects: first evidence of pollinivory and its evolutionary significance

Uniquely preserved pollen was extracted from intestines of fossil insects from the Lower Permian of the Urals. A species of Hypoperlidae, an extinct family ancestral to bark-lice, bugs and plant-hoppers, and two species of Grylloblatida, a predominantly Permian group with a few extant representatives related to stoneflies, contain protosaccate taeniate grains of several pollen genera well known as dispersed microfossils and occasionally found in sporangia of conifers, peltasperms and glossopterids. This is so far the earliest direct evidence of pollinivory, a major factor of plant-insect coevolution. The partly digested pollen grains reveal infratectal reticulum and other structural details of evolutionary significance. It is suggested that the peculiar taeniate pollen of worldwide distribution in the Permian might simultaneously evolve in several groups of Paleozoic seed plants in relation to pollinivory that, by altering the rnicropyle load and thereby the pollen/ovule ratio, could also affect ovuliferous structures. Thus pollinivory might impel rapid diversification of gymnosperms in the Permian. The pollinivorous Hypoperlidae, which have evolved in the direction of ovulivory, might initiate insect pollination in the process.     

Evolution of oil-producing trichomes in Sisyrinchium (Iridaceae): insights from the first comprehensive phylogenetic analysis of the genus

Background and Aims

Sisyrinchium (Iridaceae: Iridoideae: Sisyrinchieae) is one of the largest, most widespread and most taxonomically complex genera in Iridaceae, with all species except one native to the American continent. Phylogenetic relationships within the genus were investigated and the evolution of oil-producing structures related to specialized oil-bee pollination examined.

Methods

Phylogenetic analyses based on eight molecular markers obtained from 101 Sisyrinchium accessions representing 85 species were conducted in the first extensive phylogenetic analysis of the genus. Total evidence analyses confirmed the monophyly of the genus and retrieved nine major clades weakly connected to the subdivisions previously recognized. The resulting phylogenetic hypothesis was used to reconstruct biogeographical patterns, and to trace the evolutionary origin of glandular trichomes present in the flowers of several species.

Key Results and Conclusions

Glandular trichomes evolved three times independently in the genus. In two cases, these glandular trichomes are oil-secreting, suggesting that the corresponding flowers might be pollinated by oil-bees. Biogeographical patterns indicate expansions from Central America and the northern Andes to the subandean ranges between Chile and Argentina and to the extended area of the Paraná river basin. The distribution of oil-flower species across the phylogenetic trees suggests that oil-producing trichomes may have played a key role in the diversification of the genus, a hypothesis that requires future testing.     

海南三七（姜科）的食源性欺骗传粉

有花植物为繁殖成功,进化出各种各样的花部特征来吸引传粉者,如为传粉者提供花蜜、花粉、栖息地等,然而在33科146属的被子植物中也存在着不提供任何报酬而欺骗昆虫为其传粉的现象。这种欺骗性传粉模式主要出现在高度进化的具有多样化传粉模式的兰科植物中。报道了在姜科植物中首次发现的食源性欺骗传粉模式。对姜科山柰属海南三七进行连续2年的传粉生物学观察和研究发现,海南三七的花在早上5:30～6:00之间开放,下午17:00～18:00左右闭合萎蔫,持续大约11～12h。开花过程中花粉活性与柱头可受性均保持较高水平(>90%)。花粉/胚珠比率(P/O)为82.20±47.89(n=20)。木蜂是其主要的访花和传粉昆虫,访花目的是吸取花蜜。海南三七虽有细长线形的蜜腺,但并不分泌花蜜作为传粉昆虫访花的报酬,采用食源性欺骗的方式欺骗木蜂为其传粉。繁育系统的研究表明广西弄化的海南三七居群主要是通过根茎进行无性繁殖。     

Rush hour at the Museum – Diversification patterns provide new clues for the success of figs (Ficus L., Moraceae)

Tropical rainforests harbour much of the earth's plant diversity but little is still known about how it evolved and why a small number of plant genera account for the majority. Whether this success is due to rapid turnover or constant evolution for these hyper-diverse plant genera is here tested for the species-rich genus Ficus L. (figs). The pan-tropical distribution of figs makes it an ideal study group to investigate rainforest hyper-diversification patterns. Using a recently published, dated and comprehensive phylogenetic hypothesis, we infer that figs are an old lineage that gradually accumulated species and exhibits very low extinction rates, which corresponds to the ‘museum model’ of evolution. Overall, no major significant shifts in evolutionary dynamics are detected, yet two shifts with lower probability are found. Hemi-epiphytism, monoecy, and active pollination are traits that possibly are associated with the hyper-diversity found in figs, making it possible for the plants to occupy new niches followed by extensive radiation over evolutionary time scales. Figs possess unique diversification patterns compared to other typical rainforest genera.     

New insights into DNA barcoding of seagrasses

Taxonomists find some plant genera challenging because of the few morphological differences or unclear characters among closely related species, which leads to the misidentification of taxa. DNA barcoding is an approach to identify species by using short orthologous DNA sequences, known as ‘DNA barcodes’. Concatenated rbcL and matK sequences are considered DNA barcodes for seagrasses. However, these markers are not applicable to all members of seagrasses at the species level, especially within the genus Halophila. Our previous studies indicated that the internal transcribed spacer (ITS) showed higher species resolution than the concatenated rbcL and matK sequences in the case of Halophila ovalis and closely related species. In this study, 26 ITS, two rbcL and two matK consensus sequences from 18 seagrass taxa belonging to four families collected in India, Vietnam, Germany, Croatia and Egypt were processed. Molecular ITS analysis resolved five clades. The results also indicate that the Cymodoceaceae family might be a non-monophyletic group. In conclusion, ITS could be applied as a DNA barcode for seagrasses instead of the rbcL/matK system previously proposed.     

The evolution of tachinid pollination in Neotinea ustulata is related to floral cuticular composition and the combined high relative production of (Z)-11-C23/C25enes

Among terrestrial orchids, and particularly among the subtribe Orchidinae, flies are underrepresented as pollinators. The European Neotinea ustulata, which developed specialized pollination by tachinid flies, is known to produce high relative concentrations of the floral cuticular alkenes (Z)-11-tricosene and (Z)-11-pentacosene (referred to as (Z)-11-C23/C25enes), which seem to be uncommon among orchid flowers. If the evolution of tachinid pollination is related to that of (Z)-11-C23/C25enes, we can expect that closely related species have a different floral chemical pattern and significantly small or no production of (Z)-11-C23/C25enes, independently of their pollinator guild identity (e.g., bees, flies, moths). We chemically compared the floral cuticular composition among Neotinea species, performed electrophysiological analyses, reconstructed the phylogenetic Orchidinae tree, and identified the evolutionary history of pollinator guild and (Z)-11-C23/C25enes production within the Orchidinae. Neotinea ustulata has evolved a markedly different floral cuticular composition compared to other Neotinea and produces both compounds ((Z)-11-C23/C25enes) in high relative quantities (i.e., above 8% in combination), which are detectable by tachinid antennae. Moreover, most Orchidinae taxa have minimal or no production of these alkenes, independently of the identity of their pollinator guild. Our ancestral reconstruction suggested that (Z)-11-C23/C25enes production was an evolutionary exaptation in Neotinea, whereas tachinid pollination was a unique evolutionary innovation for N. ustulata. Floral cuticular composition and, in particular, the combined production of (Z)-11-C23/C25enes at relatively high concentrations is intimately linked to the evolution of tachinid pollination within the Orchidinae.     

Nectar spur evolution in the Mexican lobelias (Campanulaceae: Lobelioideae)

Phylogenetic studies are often hampered by the independent evolution of characters that may potentially obscure relationships. The adaptive significance of the nectar spur and its evolution within the Mexican lobeliads (Campanulaceae) is considered here. The taxonomic delimitations of Heterotoma from the Mexican species within the genera Lobelia and Calcaratolobelia were tested. Independent molecular data were gathered to determine whether the Mexican spurred lobeliads should be treated as distinct genera. The internal transcribed spacer (ITS) region from 18-26S nuclear rDNA and chloroplast DNA from the 3' trnK intron were sequenced from 14 representative species. Our data suggest that Heterotoma, as originally conceived, is a good evolutionary unit within Lobelia and that the presence of a nectar spur is an important morphological character that can be used in defining phylogenetic position. This study also suggests that morphological changes associated with hummingbird pollination have evolved more than once in the Mexican lobeliads, from small blue-flowered, insect-pollinated relatives.     

Phylogenetic insights into the correlates of dioecy in meadow-rues (Thalictrum, Ranunculaceae)

Numerous studies have examined the evolution of sexual systems in angiosperms, but few explore the interaction between these and the evolution of pollination mode. Wind pollination is often associated with unisexual flowers, but which evolved first and played a causative role in the evolution of the other is unclear. Thalictrum, meadow-rues (Ranunculaceae), provides a unique opportunity to study the evolution of these traits because it contains insect and wind pollination and four sexual systems. We used a phylogenetic approach to reconstruct ancestral states for sexual system, pollination mode, and geographic distribution in Thalictrum, and tested for correlations to uncover the factors involved in the evolution of unisexuality and wind pollination. Our results show that dioecy, andro- and gynomonoecy evolved at least twice from hermaphroditism. Wind pollination, unisexual flowers, and New World distribution were all significantly correlated. Wind pollination may have evolved early in the genus, followed by multiple losses and gains, and likely preceded the origin of unisexual flowers in several cases; we found no evidence for unisexual flowers evolving prior to wind pollination. Given a broad scale study showing the evolution of dioecy before wind pollination, our results from a finer scale analysis highlight that different evolutionary pathways are likely to occur throughout angiosperms.     

Phylogenetic analysis of the class Sporozoea (phylum Apicomplexa Levine, 1970): evidence for the independent evolution of heteroxenous life cycles

A phylogenetic analysis of representative genera in the class Sporozoea was undertaken using biological and morphological features to infer evolutionary relationships among the widely recognized groups in the class. Gregarines were used as a functional outgroup to the remaining sporozoa (adeleids, eimeriorins, haemosporinids, and piroplasms). The piroplasms were shown to be closely related to the adeleid parasites. Species of Babesia and Theileria were shown not to form a sister group to the haemosporinids as has been frequently suggested. The data indicate that the biologically diverse family Haemogregarinidae should be divided into at least 3 families (Haemogregarinidae Neveu-Lemaire, 1901, containing the genera Haemogregarina and Cyrilia; Karyolysidae Wenyon, 1926, containing the genus Karyolysus; Hepatozoidae Wenyon, 1926, containing the genus Hepatozoon) because the 4 genera currently within the family do not form a monophyletic group. Correlation between parasite phylogeny and taxonomic affinities of their definitive hosts suggests that the definitive hosts of heteroxenous sporozoa are their ancestral hosts. Heteroxenous sporozoan life cycles apparently have evolved independently to adapt to changes in the feeding behaviors of their definitive hosts.