Author: Aryeh Miller Page 2 of 3

In 1891, Elio Modigliani–an Italian biologist from Florence–collected an odd, male agamid lizard from northern Sumatra (type locality listed as “Si-Rambé Forest”). The specimen was brought back to Italy, and cataloged in the Museo Civico di Storia Naturale di Genova (Genova, Italy). More than 40 years later, this single specimen was described by Vinciguerra (1933) as Harpesaurus modiglianii. In his original description, Vinciguerra (1933) notes this Sumatran individual is a “notable lizard that is worth to be known,” and that it can be identified through a “[rostral appendage] as long as the head, simple, formed by a sickle-shaped compressed scale, upward and with its basis surrounded by some rather large scales” (Putra et al. 2020). It would be an injustice if I didn’t include the lovely plate featured in Vinciguerra’s original description (see below).

Vinciguerra’s 1933 illustration from his description of Harpesaurus modiglianii. After Modigliani’s collection of a single specimen, the species would be presumed extinct, and not seen again until 2018, just north of Toba Lake in Sumatra! The rediscovery was documented and published by Putra et al. (2020).

Though not seen again for another 129 years, Harpesaurus modiglianii is just one of several remarkable rostral appendage bearing lizards distributed throughout the world. Moreover, the story of H. modiglianii as an enigma to the herpetologists of Southeast Asia is not an unfamiliar one, as a congener–Harpesaurus tricinctus–faces a similar predicament, having not been seen since 1851! Still, importantly, interest in this group, and other rostral appendage bearing lizards, remains strong. As such, a critical question remains– just what exactly does the rostral appendage do? How might it relate to the ecology of these lizards? In a new paper in Salamandra, Ivan Ineich and colleagues discuss these topics exactly across a wide phylogenetic breadth, from Harpesaurus, to Calumma, to Anolis. Give it a read, and check out these amazing lizards!

 

New literature alert!

Pinocchio lizards and other lizards bearing rostral appendages − the peculiar habitus of the draconine agamid Harpesaurus tricinctus with highlights on its ecological implications and convergence with its New World equivalent, the dactyloid Anolis proboscis

In Salamandra

Ineich, Koppetsch, and Böhme (2022)

Abstract:

Vinciguerra, D. 1933. Descrizione di una nuova specie di Harpesaurus di Sumatra. Ann. Mus. civ. stor. nat. Genova 56: 355-357.

Anolis porcatus is the most recent Caribbean anole to have been documented to consume and disperse seeds. Natural history research by Armas (2022) observes A. porcatus feeding on West Indian holly, and finds successful germination of the fecal pellets. Credit Thomas Brown (Wikimedia Commons).

Recent research on Anolis lizards has suggested their omnivorous tendencies might aid in the dispersal of seeds. Most recently, this was discussed by Giery et al. (2017), who reported Cuban Knight Anoles (A. equestris) to consume and disperse royal palms. This year, Armas (2022) reports Anolis porcatus consumes and disperses West Indian holly. Check it out!

New literature alert!

Consumption and Dispersal of West Indian Holly (Turnera ulmifolia, Turneraceae) Seeds by Cuban Green Anoles, Anolis porcatus (Squamata: Dactyloidae)

In Reptiles & Amphibians

Armas (2022)

Literature Cited:

de Armas, L. F. (2022). Consumption and Dispersal of West Indian Holly (Turnera ulmifolia, Turneraceae) Seeds by Cuban Green Anoles, Anolis porcatus (Squamata: Dactyloidae). Reptiles & Amphibians, 29(1), 115-116.

Giery, S. T., Vezzani, E., Zona, S., & Stroud, J. T. (2017). Frugivory and seed dispersal by the invasive knight anole (Anolis equestris) in Florida, USA. Food Webs, 11, 13-16.

An Anolis biporcatus enjoys some sun while balancing along a branch with the help of those neat adhesive toepads and claws.  Credit Wikimedia Commons.

In a recently published study, Cortés-Parra et al. (2021) compare the claws and toepads of mainland and island Anolis radiations in examination of “morphotype” diversity across phylogenetic and ecological scales. This study intersects nicely with quite recent work comparing the mainland and island radiations (e.g., Hiue et al. 2021; Patton et al. 2021), and claw morphology (e.g., Yuan et al. 2019, 2020; Falvey et al. 2020).

New literature alert!

Claws and toepads in mainland and island Anolis (Squamata: Dactyloidae): Different adaptive radiations with intersectional morphospatial zones

In Journal of Anatomy

Cortés-Parra, Calderón-Espinosa, and Jerez

Abstract:

Cortés‐Parra, C., Calderón‐Espinosa, M. L., & Jerez, A. (2021). Claws and toepads in mainland and island Anolis (Squamata: Dactyloidae): Different adaptive radiations with intersectional morphospatial zones. Journal of anatomy.

Falvey, C. H., Aviles-Rodriguez, K. J., Hagey, T. J., & Winchell, K. M. (2020). The finer points of urban adaptation: intraspecific variation in lizard claw morphology. Biological Journal of the Linnean Society, 131(2), 304-318.

Huie, J. M., Prates, I., Bell, R. C., & de Queiroz, K. (2021). Convergent patterns of adaptive radiation between island and mainland Anolis lizards. Biological Journal of the Linnean Society, 134(1), 85-110.

Patton, A. H., Harmon, L. J., del Rosario Castañeda, M., Frank, H. K., Donihue, C. M., Herrel, A., & Losos, J. B. (2021). When adaptive radiations collide: Different evolutionary trajectories between and within island and mainland lizard clades. Proceedings of the National Academy of Sciences, 118(42).

Yuan, M. L., Wake, M. H., & Wang, I. J. (2019). Phenotypic integration between claw and toepad traits promotes microhabitat specialization in the Anolis adaptive radiation. Evolution, 73(2), 231-244.

Yuan, M. L., Jung, C., Wake, M. H., & Wang, I. J. (2020). Habitat use, interspecific competition and phylogenetic history shape the evolution of claw and toepad morphology in Lesser Antillean anoles. Biological Journal of the Linnean Society, 129(3), 630-643.

Anolis cristatellus (pictured; Wikimedia Commons) continues to prove itself as a model organism for examining thermal biology evolution, particularly in a comparative context of forest versus city-dwelling populations. Recent research by Campbell-Staton et al. (2021) aims to uncover how differential gene expression modulates adaptive and maladaptive plasticity in these populations.

In a recently published study, Shane Campbell-Staton and company continue their comparative investigation of urban-forest anole thermal biology. Employing a combination of wild-caught and common-garden-reared urban and forest populations of Anolis cristatellus, Campbell-Staton et al. (2021) tease apart the role of selection in mediating adaptive and maladaptive thermal tolerance plasticity using a fine-toothed transcriptomic comb.

New literature alert!

Selection on adaptive and maladaptive gene expression plasticity during thermal adaptation to urban heat islands

In Nature Communications

Campbell-Staton, Velotta, and Winchell

Abstract

An illustration from Gosse (1851) depicting Jamaica’s crown-giant, Anolis garmani (note that Gosse used the old name, “Dactyloa Edwardsii”), adjacent to a West Indian boid (Chilabothrus).

Jamaica’s six endemic Anolis species–A. garmani, A. reconditus, A. valencienni, A. lineatopus, A. grahami, and A. opalinus–have long captured the fascination of Caribbean naturalists. And how could they not? Although only six, these lizards are among the Caribbean’s most eye-grabbing. Take it from Phillip Henry Gosse, who recounted his experience catching one of these six species using a twine lasso in A Naturalist’s Sojourn in Jamaica (1851):

“The mode in which I formed an acquaintance with the species may be worthy of being related. One day in February, having ascended the ridge with a companion, my attention was arrested by a Lizard about a foot long, and of a lively green colour, on the trunk of a small tree, head downward, intently watching our motions as we stood near. My young friend suggested the possibility of capturing it by slipping a noose over its head, while its attention was engaged by whistling. I laughingly proceeded to try the spell; and having made a noose of small twine, which I tied to the end of a switch, I gently walked towards him, whistling a lively tune. To my astonishment he allowed me to slip the noose over his head, merely glancing his bright eye at the string as it passed. I jerked the switch; the music ceased; and the green-coated forester was sprawling in the air, dangling, greatly to his annoyance, at the end of my string. He was very savage, biting at every thing near; presently his colour began to change from green to blackish, till it was of an uniform bluish black with darker bands on the body, and a brownish black on the tail: the only trace of green.”

Since Gosse’s work on West Indian reptiles (including formal designation of the Jamaican anole radiation as Placopsis), much has changed in our understanding of Jamaica’s Anolis diversity and evolution. In 2002, Todd Jackman and colleagues published a study aiming to estimate the phylogenetic relationships among Jamaica’s anoles.

The authors found support for the following topology (Jackman et al. 2002; Fig. 7): A. lineaotopus and A. reconditus form a clade that is sister to the remaining Jamaican anoles, followed by A. valencienni, A. garmani, and, ultimately, A. grahami + A. opalinus. Jackman et al. would continue in the same paper to discuss phylogeography and intraspecific divergences. Notably, a single A. opalinus from Hardwar Gap (Blue Mountains) appeared to be more closely allied to A. valencienni than to other sampled A. opalinus individuals. This diverse array of mitochondrial haplotypes recovered from A. opalinus then raises the question, does the history of Anolis on Jamaica involve hybridization, or is it merely a result of incomplete lineage sorting we may expect from a rapid adaptive radiation?

Nearly twenty years went by without an answer. Was the phylogenetic hypothesis posited by Jackman et al. correct? What’s going on with A. opalinus? Separately, in the two decades since the work by Jackman and colleagues, a revolution has occurred in phylogenetic biology. In the study of phylogeny, if introgression (e.g., ancient mitochondrial capture as a result of hybridization) has played a role in shaping the evolutionary history of the relevant group, it’s important that we test if such events have occurred, and subsequently be able to disentangle and ultimately account for them in our phylogenetic estimations. Failure to do so can lead to misleading topologies, inaccurate reconstructions of evolutionary histories and parameter estimates, as well as shortcomings in accurately describing and recognizing biodiversity.

Luckily, resolution to this issue has been afforded by several folks (Claudia Solís-Lemus and Cécile Ané, to name just two) who have developed statistical methods to detect and account for both incomplete lineage sorting (ILS) and reticulate patterns of evolution (introgression). So, how does this relate to those oh-so-cool Jamaican anoles? This is where Myers et al. (2021) come in.

In a new study in the Spotlight section of Systematic Biology, Myers and colleagues re-open the investigation into Jamaican Anolis phylogeny using the aforementioned suite of novel methods. For those in attendance at the Joint Meeting of Herpetologists and Ichthyologists in 2018, the early stages of this work were presented by students conducting research at the American Museum of Natural History, previously featured on Anole Annals. Using genotyping-by-sequencing (an approach that has been applied elsewhere in Anolis research), the authors generate swaths of SNP data from the nuclear genome. To be exact, the total dataset comprised 257,317 base pairs (just over 2,900 loci). Restriction-site-associated approaches (i.e., RAD-Seq) to sequencing DNA have made it feasible to capture large, representative samples of the nuclear genome at low cost.

Armed with data from both the nuclear and mitochondrial genomes, Myers et al. (2021) found dramatically different relationships and evolutionary histories among species between the two sources. Figure 3 demonstrates this disparity well, and further hammers home the general dangers of violating model assumptions in phylogenetic inference (in this case, the multi-species coalescent [MSC] model, which assumes a lack of gene flow among sampled taxa).

First, when using solely the mtDNA data in a MSC framework, the authors find A. opalinus from the Blue Mountains to be polyphyletic, a result concordant with the inference of Jackman et al. (2002). Specifically, one A. opalinus lineage (Blue Mountains) is sister to A. valencienni, whereas the other A. opalinus lineage is sister to A. grahami. Notably, the time calibrated mtDNA gene-tree suggests the two A. opalinus mtDNA genomes are more than 30 million years divergent!

The authors then infer a species tree using the GBS data in an MSC framework (one that assumes gene-tree species-tree discordance can be attributed to incomplete lineage sorting and accounts for such). With this tree, the two A. opalinus lineages form a clade sister to A. grahami and A. garmani. Finally, with SnaQ (a modeling program developed by Solís-Lemus and colleagues to infer reticulation events across a tree), the authors recovered an identical topology to the nuclear DNA based species-tree, but with high support for a single introgression event (and hence, reticulate evolution) between A. opalinus and A. grahami. Using simulations, Myers and colleagues provide evidence against ILS as the causative agent for gene-tree species-tree discordance, favoring hybridization as the culprit.

I won’t spoil the Discussion, but much of Jamaican Anolis evolution remains open-ended (including the role of adaptive introgression in shaping Anolis communities). It’s probably safe to say Gosse wasn’t pondering the possibility of adaptive introgression in shaping Jamaican Anolis phylogeny. However, resolution of the outstanding questions identified by Myers et al. (2021) will come primarily through Gosse’s philosophy–getting out in the field, catching lizards, and getting a more-fine scale, phylogeographic picture of the variation over space and time in Jamaican Anolis.

I thank Ed Myers and Kevin de Queiroz for feedback on this blog post.

Literature Cited:

Jackman, T. R., Irschick, D. J., De Queiroz, K., Losos, J. B., & Larson, A. 2002. Molecular phylogenetic perspective on evolution of lizards of the Anolis grahami series. Journal of Experimental Zoology 294(1) 1-16.

New literature alert!

Interspecific Gene Flow and Mitochondrial Genome Capture During the Radiation of Jamaican Anolis Lizards (Squamata; Iguanidae)

In Systematic Biology

Myers, Mulcahy, Falk, Johnson, Carbi, de Queiroz

Gene flow and reticulation are increasingly recognized as important processes in the diversification of many taxonomic groups. With the increasing ease of collecting genomic data and the development of multispecies coalescent network approaches, such reticulations can be accounted for when inferring phylogeny and diversification. Caribbean Anolis lizards are a classic example of an adaptive radiation in which species have independently radiated on the islands of the Greater Antilles into the same ecomorph classes. Within the Jamaican radiation at least one species, A. opalinus, has been documented to be polyphyletic in its mitochondrial DNA, which could be the result of an ancient reticulation event or incomplete lineage sorting. Here we generate mtDNA and genotyping-by-sequencing (GBS) data and implement gene-tree, species-tree, and multispecies coalescent network methods to infer the diversification of this group. Our mtDNA gene-tree recovers the same relationships previously inferred for this group, which is strikingly different from the species-tree inferred from our GBS data. Posterior predictive simulations suggest that our genomic data violate commonly adopted assumptions of the multispecies coalescent model, so we use network approaches to infer phylogenetic relationships. The inferred network topology contains a reticulation event but does not explain the mtDNA polyphyly observed in this group, however coalescent simulations suggest that the observed mtDNA topology is likely the result of past introgression. How common a signature of gene flow and reticulation is across the radiation of Anolis is unknown; however, the reticulation events that we demonstrate here may have allowed for adaptive evolution, as has been suggested in other, more recent adaptive radiations.

In a recent study in the Proceedings of the National Academy of Sciences, Bock et al. (2021) conduct a genomic and phenotypic appraisal of adaptive evolution and invasion biology of Anolis sagrei (Wikimedia Commons).

In 2004, Jason Kolbe and colleagues published a now-classic invasion biology study in Nature, mapping out the population genetics of invasive Anolis sagrei populations. Using approximately 1,200 bp of mtDNA sequence data (ND2 and adjacent tRNAs), Kolbe et al. examined the evolutionary origins of the Brown Anole in its journey out of its ancestral area (Cuba), and into a broad invasive range. In several out-of-Cuba dispersal events that formed the collective invasive Brown Anole in Florida, Kolbe et al. (2004) found that invasion had actually increased genetic diversity within these populations, far greater than that observed in the native range. Furthermore, many of the global invasive populations of A. sagrei (e.g., Taiwan, Grenada), sourced from Florida, had maintained comparably high levels of genetic diversity. Hence, the work by Kolbe et al. demonstrated that the repeated introduction of multiple, evolutionarily diverse lineages derived from the native range and subsequently injected into a novel range may be a key force in driving successful invasion.

If we fast-forward five years to 2009, two years prior to the release of the A. carolinensis genome, Chris Schneider publishes a paper in Integrative and Comparative Biology (Schneider 2009) titled “Exploiting genomic resources in studies of speciation and adaptive radiation of lizards in the genus Anolis.” In his paper, Schneider discusses the unique opportunity that lies ahead in understanding evolutionary theory through the lens of Anolis genomic resources. Schneider’s vision—as I perceive it—was one that sought to excite the evolutionary ecology community about the wonderful opportunities ahead that Anolis lizards present in understanding, most broadly, the genetic basis of adaptation.

Now, in 2021, more than 15 years after the study by Kolbe et al., Bock et al. (2021) return for an integrative evolutionary investigation of A. sagrei throughout Florida using a recently generated reference genome and corresponding morphological data. In line with Schneider’s (2009) perspective, Bock et al. (2021) tell a captivating story of adaptation, genome biology, and invasion. Wielding the power of one of the most contiguous and complete squamate genomes assembled to date (more on that another time!), the authors identified a large-effect locus posited to be responsible for adaptive shifts in limb length, which in turn provides insight into how natural selection can modulate hybridization during the course of biological invasion.

New literature alert!

Changes in selection pressure can facilitate hybridization during biological invasion in a Cuban lizard

In PNAS

Bock, Baeckens, Pita-Aquino, Chejanovski, Michaelides, Muralidhar, Lapiedra, Park, Menke, Geneva, Losos, and Kolbe

Abstract

Literature cited:

Kolbe, J. J., Glor, R. E., Schettino, L. R., Lara, A. C., Larson, A., & Losos, J. B. 2004. Genetic variation increases during biological invasion by a Cuban lizard. Nature 431(7005): 177-181.

Schneider, C. J. 2008. Exploiting genomic resources in studies of speciation and adaptive radiation of lizards in the genus Anolis. Integrative and Comparative Biology 48(4): 520-526.

In a new study published in the Proceedings of the National Academy of Sciences, Patton et al. (2021) examine island and mainland radiations of Anolis lizards in an effort to understand what occurs when “adaptive radiations collide.” Discussion of mainland anoles merits featuring one of the oddest mainland species, the Ecuadorian Anolis proboscis (female and male pictured here; credit Santiago Ron [Wikimedia Commons]).

New literature alert!

Upon hearing “anole lizards,” those in the evolution and ecology community familiar with the outstanding diversity of Anolis lizards may immediately reflect on the replicative adaptive radiations that have occurred in the Greater Antilles, painting a portrait of adaptation, convergence, and ecological character displacement that has served as the basis of research among Caribbean biologists for decades. But, perhaps, what is less generally appreciated is that the vast bulk of Anolis lizard diversity (currently sitting at 436 species, per the ReptileDatabase) actually occurs on mainland Central and South America! Indeed, if we were to zoom out on the Anolis Tree of Life, we could pick out three major clades that represent independent adaptive radiations– one in the Greater and Lesser Antilles, and then two on the Mainland. Hence, as has been appreciated by many Anolis biologists before (most recently, Huie et al. 2021), the multiple radiations of these lizards provides the substrate to examine not only convergence, but, additionally, what happens when these clades come into contact? What happens when adaptive radiations collide?

This question forms the basis (and title) for a recently published study by Patton et al. (2021), who attempt to untangle themes of adaptation, historical biogeography, convergence and divergence in ecology and morphology, and the diversification dynamics of the three major Anolis radiations.

When adaptive radiations collide: Different evolutionary trajectories between and within island and mainland lizard clades

In PNAS

Patton, Harmon, Castañeda, Frank, Donihue, Herrel, and Losos

Abstract:

Oceanic islands are known as test tubes of evolution. Isolated and colonized by relatively few species, islands are home to many of nature’s most renowned radiations from the finches of the Galápagos to the silverswords of the Hawaiian Islands. Despite the evolutionary exuberance of insular life, island occupation has long been thought to be irreversible. In particular, the presumed much tougher competitive and predatory milieu in continental settings prevents colonization, much less evolutionary diversification, from islands back to mainlands. To test these predictions, we examined the ecological and morphological diversity of neotropical Anolis lizards, which originated in South America, colonized and radiated on various islands in the Caribbean, and then returned and diversified on the mainland. We focus in particular on what happens when mainland and island evolutionary radiations collide. We show that extensive continental radiations can result from island ancestors and that the incumbent and invading mainland clades achieve their ecological and morphological disparity in very different ways. Moreover, we show that when a mainland radiation derived from island ancestors comes into contact with an incumbent mainland radiation the ensuing interactions favor the island-derived clade.

Phelsuma laticauda steals the reptilian spotlight on Anole Annals today. This Day Gecko, alongside Anolis carolinensis and A. sagrei, are the focus of a recently conducted  comparative study by Wright et al. (2021) examining the linkage between morphology, performance, and ecology relative to the usage of adhesive digital toepads. Credit Wikimedia Commons.

New literature alert!

A new study by Wright et al. (2021) published in Functional Ecology presents the results of an ambitious and exciting experimental study comprising greater than 9,000 habitat use observations to compare how clinging performance interacts with ecology in Anolis lizards and the iconic Phelsuma laticauda (Day Gecko). The two anoles–A. carolinensis and A. sagrei–along with P. laticauda, have invaded the once squamate-free community of Hawaiʻi, providing the substrate for Wright et al. to examine the interaction between performance, morphology, and ecology.

Clinging performance on natural substrates predicts habitat use in anoles and geckos

 In Functional Ecology

Wright, Kennedy-Gold, Naylor, Screen, Piantoni, and Higham,

Abstract:

1) For arboreal lizards, the ability to cling or adhere to the substrate is critical for locomotion during prey capture, predator escape, thermoregulation, and social interactions. Thus, selection on traits related to clinging is likely strong.

2) Correlations between morphology, performance, and habitat use have been documented in arboreal lizards, providing a framework for using functional traits to predict habitat use in the field.

3) We tested the hypothesis that clinging performance predicts habitat use in an actively assembling community of introduced lizards in Hawaiʻi comprised of anoles (Anolis carolinensis, A. sagrei) and day geckos (Phelsuma laticauda).

4) We measured morphological traits (toepad area and lamellae number) and tested clinging performance on two artificial and eight natural substrates in the lab. We measured habitat use in 10 m x 10 m outdoor enclosures where habitat availability was controlled and the lizard species assemblage was manipulated to reflect all species combinations. The enclosure experiment generated more than 9,000 habitat use observations from 360 lizards.

5) Morphological traits that predict performance in Anolis were not predictive in Phelsuma, indicating that direct measures of performance are necessary for comparisons between the genera.

6) Measuring clinging performance on multiple substrates provided key insights into patterns of habitat use. While all three species performed best on an artificial smooth substrate (acrylic), performance on natural substrates predicted which texture (rough vs. smooth) was most often used by each species.

7) Performance predicted perch height use: species with the greatest clinging performance (A. carolinensis and P. laticauda) across substrates perched twice as high as A. sagrei.

8) We did not observe habitat shifts in the height or texture of perches used by any species in response to experimental manipulation of the lizard species assemblage.

9) Our results highlight the inextricable link between ecology, morphology, and performance, the importance of measuring functional traits in ecologically-relevant ways, and the potential for resource partitioning to be influenced by differences in the ability to attach to different substrates.

In a new study hot off the press at Evolution, Stuart and colleagues experimentally test the dimorphism-richness hypothesis using several mangrove islands in south Florida inhabited by Anolis carolinensis (pictured; credit Wikimedia Commons) and A. sagrei.

New literature alert!

Male and female Anolis carolinensis maintain their dimorphism despite the presence of novel interspecific competition

In Evolution

Stuart, Sherwin, Kamath, and Veen

Abstract:

Natural selection favors sexual dimorphism that reduces resource competition between the sexes of the same species. However, niche partitioning among interspecific competitors should counter such divergence, as partitioning the niche results in smaller total niche widths for each individual species, leaving less room for the sexes to diverge. A straightforward (and long-standing) hypothesis emerges: species in competitor-rich ecological communities should show less sexual dimorphism than species in competitor-poor ecological communities. Here, we test this prediction using a well-documented natural experiment generated by the recent arrival of Anolis sagrei to a set of small islands in Mosquito Lagoon, Florida, containing Anolis carolinensis. Despite known interspecific habitat partitioning and rapid evolution in habitat-use traits by A. carolinensis in this system, sexual dimorphism between male and female A. carolinensis was not reduced as predicted on two-species islands relative to islands with only A. carolinensis. This is consistent with a small but growing body of empirical tests of the dimorphism-richness hypothesis that have been ambiguous in their support at best. A rethinking of the validity of this intuitive hypothesis is needed.

Anolis sagrei (pictured) is the star of a new study by Kahrl et al. (2021) examining selection pressures on sperm. Credit Wikimedia Commons.

New literature alert!

Selection on Sperm Count, but Not on Sperm Morphology or Velocity, in a Wild Population of Anolis Lizards

In Cells

Kahrl, Kustra, Reedy, Bhave, Seears, Warner, and Cox

Abstract:

Sperm competition is a widespread phenomenon that shapes male reproductive success. Ejaculates present many potential targets for postcopulatory selection (e.g., sperm morphology, count, and velocity), which are often highly correlated and potentially subject to complex multivariate selection. Although multivariate selection on ejaculate traits has been observed in laboratory experiments, it is unclear whether selection is similarly complex in wild populations, where individuals mate frequently over longer periods of time. We measured univariate and multivariate selection on sperm morphology, sperm count, and sperm velocity in a wild population of brown anole lizards (Anolis sagrei). We conducted a mark-recapture study with genetic parentage assignment to estimate individual reproductive success. We found significant negative directional selection and negative quadratic selection on sperm count, but we did not detect directional or quadratic selection on any other sperm traits, nor did we detect correlational selection on any trait combinations. Our results may reflect pressure on males to produce many small ejaculates and mate frequently over a six-month reproductive season. This study is the first to measure multivariate selection on sperm traits in a wild population and provides an interesting contrast to experimental studies of external fertilizers, which have found complex multivariate selection on sperm phenotypes.