Tim Mitchell, Josh Hall, and Daniel Warner: Seasonal Shifts in Anolis sagrei Reproduction Invoke Challenges for Scientific Reproducibility
Sometimes a scientist just needs hundreds of hatchling anoles for an experiment. Tim Mitchell found himself in this position recently, and, like a good lizard ecologist, he started breeding colonies of anoles in the lab to produce eggs to incubate until hatching. As he created three different breeding colonies from brown anoles (Anolis sagrei) in central Florida, one each in February, June, and September, Tim found that he had also created an ideal situation in which to examine how the reproductive condition and output of brown anoles varies across the breeding season.
Tim, along with his coauthors Josh Hall and Dan Warner, found that females produced eggs with significantly greater mass later in the breeding season. These eggs took longer to produce than those earlier in the year (a greater interclutch interval), and the eggs resulted in hatchlings that had higher mass in relation to the weight of their eggs. These reproductive differences remained even after accounting for the fact that female anoles were also larger and heavier later in the year.
These findings suggest that female A. sagrei may shift their reproductive effort from producing a higher quantity of eggs (i.e., more, smaller eggs resulting in smaller hatchlings) in the beginning of the breeding season, to producing higher quality eggs (i.e., fewer, larger eggs resulting in larger offspring) later in the breeding season. Tim’s findings also stress the importance of investigating and accounting for seasonal differences when examining reproductive output in lizards.
Effect of perch treatment on (A) latency to reproduce and (B) yolk corticosterone.
Competition for perches has been an important factor in the diversification of anoles. Yet, we know little about the influence of perch availability on reproduction. To address this, Dan Warner, Matt Lovern, and I housed male / female pairs of brown anoles (Anolis sagrei) in treatments with either high- or low-availability of perches (Fig. 1).
We found that females reduced how often they used perches when perches were limited. More interestingly, though, when perches were limited, females tended to take longer to begin laying eggs (for the first time in a season; p = 0.063, Fig. 2A) and allocated more corticosterone to egg yolk (p = 0.069, Fig. 2B), although these findings were not statistically significant.
Figure 2. Effect of perch treatment on (A) latency to reproduce and (B) yolk corticosterone.
In many habitats in which brown anoles occur, organic perches are abundant and not likely to be limited. However, in urban areas or on some islands anoles have colonized, perches can be limited. Our study suggests that such habitats may have consequences for reproduction.
Citation for the full paper:
Delaney, DM, MB Lovern, and DA Warner. 2016. Does reduced perch availability affect reproduction in the brown anole? An experimental test in the laboratory. Journal of Herpetology50:227-232.
In collaboration with the Conservation Biology course taught by Dr. Karen Beard here at Utah State University, where I am a Ph.D. student, I have been involved in gathering life history data on ~400 species of reptiles that have been introduced outside of their native ranges for an analysis of how life history traits (e.g., diet, fecundity, longevity) interact with other factors to influence the likelihood of successful establishment. Appendix A of Fred Kraus’ 2009 book Alien Reptiles and Amphibiansis the source of the species list we are using, and included in this analysis are 26 species of Anolis. This is where you come in.
First, we coded all anoles as (i) sexually-dichromatic, (ii) diurnal, (iii) non-venomous, (iv) oviparous, (v) omnivores that lack (vi) temperature-dependent sex determination and (vii) parthenogenesis. Is anyone aware of any exceptions to these seven generalizations?
Second, we searched for data on clutch size, clutch frequency, incubation time, and longevity. The Anole Classics section of this site and the Biodiversity Heritage Library were particularly useful. After conducting what I feel to be a pretty thorough literature scavenger hunt, I am forced to conclude that some of these data simply do not exist at the species level for all of the species we’re interested in, or are not explicitly stated in a way that is obvious to a non-anole-expert. Of course, there is a lot of literature, including many books that I don’t have access to, and there are also lots of credible observations that don’t get published. I’m hoping that some of the readership here can help fill in at least some of the blanks in the table below. As one member of the team, I did not collect all of the data that are filled in myself, nor have I personally vetted every value, so if you spot an error please do point it out.
Two important points:
Many environmental factors obviously influence the life history parameters of our beloved and wonderfully plastic reptiles, so we appreciate that many of these values would be better represented by ranges and are dependent on latitude, altitude, climate, and many other factors. Where a range is published, we are using its median value.
I should also emphasize that, because of the large size of this study and the diversity of taxa included (ranging in size from giants like Burmese Pythons, Nile Crocodiles, and Aldabra Tortoises to, well, anoles and blindsnakes), it is more important for the data to reflect the relative values of these life history parameters across all anoles (and all reptiles) than it is to specifically and precisely represent all known variation within a given species of anole.
Without further ado (for your enjoyment, and because I know from my own blog that nobody reads posts lacking pictures, I’ve embedded an image of each species):
Species
Median clutch size
Median clutches per year
Incubation time (days)
Maximum longevity (months)
A. aeneus
2
A. baleatus
A.bimaculatus
2
43
84
A. carolinensis
1.15
6
41.5
65
A.chlorocyanus
1
18
A. conspersus
1
A. cristatellus
2.5
18
83
A. cybotes
1
18
45
A. distichus
1
16
45.5
A. equestris
1
1
48
149
A. extremus
A. ferreus
1
18
A. garmani
1.5
18
67
A. grahami
1
A. leachii
A. lineatus
A. lucius
1
3.5
60
A. marmoratus
2
50
A. maynardi
A. porcatus
1
18
63.5
A. pulchellus
1
A. richardii
1
A. sagrei
2
20
32
22
A. stratulus
A. trinitatis
2
50
A. wattsi
1
Thanks in advance. I think this is a great blog and I hope to post something more interesting on here soon.
