SummaryMatrix population models (MPMs) are an important tool for biologists seeking to understand the causes and consequences of variation in vital rates (e.g., survival, reproduction) across life cycles. Empirical MPMs describe the age- or stage-structured demography of organisms and usually represent the life history of a population during a particular time frame at a specific geographic location.The COMPADRE Plant Matrix Database and COMADRE Animal Matrix Database are the most extensive resources for MPM data, collectively containing >12,000 individual projection matrices for >1,100 species globally. Although these databases represent an unparalleled resource for researchers, land managers, and educators, the current computational tools available to answer questions with MPMs impose significant barriers to potential COM(P)ADRE database users by requiring advanced knowledge to handle diverse data structures and program custom analysis functions.To close this knowledge gap, we present two interrelated R packages designed to (i) facilitate the use of these databases by providing functions to acquire, quality control, and manage both the MPM data contained in COMPADRE and COMADRE, and a user’s own MPM data (Rcompadre), and (ii) present a range of functions to calculate life history traits from MPMs in support of ecological and evolutionary analyses (Rage). We provide examples to illustrate the use of both.Rcompadre and Rage will facilitate demographic analyses using MPM data and contribute to the improved replicability of studies using these data. We hope that this new functionality will allow researchers, land managers, and educators to unlock the potential behind the thousands of MPMs and ancillary metadata stored in the COMPADRE and COMADRE matrix databases, and in their own MPM data.

Most theory on the evolution of senescence implicitly assumes that all offspring are of equal quality. However, in addition to age-related declines in survival and fecundity (classically defined senescence), many organisms exhibit age-related declines in offspring quality, a phenomenon known as a parental age effect. Theoretical work suggests that parental age effects may alter age trajectories of selection and therefore shape the evolution of senescence; however, to date, these analyses have been limited to idealized life cycles and models of maternal care in human populations. To gain a broader understanding of how parental age effects may shape age trajectories of selection, we extend the classic age-structured population projection model to also account for parental age structure and apply this model to empirical data from an aquatic plant known to exhibit parental age effects (the duckweed Lemna minor), as well as a diverse set of simulated life cycles. Our results suggest that parental age effects alter predictions from classic theory on the evolution of senescence. Age-related declines in offspring quality reduce the relative value of late-life reproduction, leading to steeper age-related declines in the force of natural selection than would otherwise be expected and potentially favoring the evolution of more rapid rates of senescence.

1. Comparative studies have demonstrated extensive variation in age trajectories of mortality and fecundity, both within and among species, with many taxa exhibiting a general pattern of age-related demographic decline referred to as senescence. Whereas a considerable body of theory is devoted to explaining the origin and persistence of senescence, the evolutionary forces underlying variation in demographic trajectories more generally remain poorly understood. 2. Studying variation in demographic trajectories is complicated by the fact that different species (or even different populations of a given species) may live and reproduce on different time-scales, which, for comparative purposes, can make it challenging to disentangle patterns of age-related demographic change (the shape of demographic age trajectories) from the time-scale on which those changes happen (the pace of demographic age trajectories). 3. Here, we examine variation in the pace and shape of demographic trajectories among strains of the aquatic plant Lemna turionifera Landolt from 24 sites across Alberta, Canada. Our main objectives were to describe the shape of demographic trajectories in L. turionifera, and test for among-strain variation in pace and shape. We also tested whether potential variation in pace and shape is (1) constrained by trade-offs with other life-history traits, and (2) consistent with local adaptation to environmental characteristics at the sites of strain origin. 4. The strains we examined were overwhelmingly subject to age-related increases in mortality and declines in fecundity, with increases in mortality tending to decelerate and plateau at advanced ages. Despite substantial among-strain variation in cumulative fecundity and plant size, measures of pace and shape did not in themselves vary significantly among strains. Both within and among strains, we observed a negative relationship between plant size and the shape of fecundity trajectories, but we found no other evidence for life-history trade-offs involving pace or shape, nor for local adaptation. 5. Synthesis. Angiosperms display remarkable demographic variation. Our results suggest that the pace and shape of demographic trajectories are highly conserved within one particular angiosperm species (Lemna turionifera), despite substantial among-strain variation in other life-history traits.

With almost 400,000 species to choose from, plant biologists seeking a study species have no shortage of raw material. In the face of such diversity, plant model systems have come to the fore in many disciplines, with Arabidopsis thaliana being the most conspicuous example. The main benefits of model systems are that they (1) are amenable to the collection of data relevant to a variety of research questions (i.e., due to intrinsic species traits such as small stature and short generation time) and (2) come with value-added properties by virtue of their history of use in research, such as well-developed experimental protocols and molecular tools, a deep and broad literature, and an international community of experts (Fox, 2012; Chang et al., 2016). While the wisdom of relying on a small number of model systems is a matter of debate, there is little doubt that working on easily studied and well understood plant species has paid off in many disciplines. Here we highlight the potential of one particular group—duckweeds—as a model system for research in the disciplines of ecology and evolution. Duckweeds are floating or submergent aquatic monocots that comprise the “simplest and smallest of flowering plants” (Hillman, 1961). Their small stature and morphological simplicity are just two of the many traits that make duckweeds well suited for addressing a variety of questions in ecology and evolution (Tables 1, 2). Furthermore, because of a long history of use in fields such as ecotoxicology (e.g., Wang, 1990) and plant development (e.g., Hillman, 1976), and ongoing interest in using duckweed for industrial applications such as feed and biofuel production (e.g., Cheng and Stomp, 2009) and bioremediation (e.g., Ziegler et al., 2016), researchers studying duckweed today benefit from a mature literature, established research procedures, repositories with hundreds of live strains, and ample molecular resources including genome sequences for Spirodela polyrhiza (Wang et al., 2014) and Lemna minor (Van Hoeck et al., 2015). Before exploring the potential of duckweeds in ecology and evolution, we briefly review their natural history (based on Landolt, 1986). Individual duckweed ramets consist of a single “frond” (also called a thallus) with between zero and several roots emanating from the lower surface, depending on the species. Fronds are tiny, with surface areas on the order of 1 mm2 to 1 cm2. Though duckweeds can flower, the vast majority of their reproduction is asexual, via meristematic pockets from which clonal daughters successively bud and detach. An individual frond may produce up to a couple dozen daughters over its life, which is typically on the order of weeks. Taxonomically, the five genera and 37 species of duckweed form a monophyletic subfamily, Lemnoideae, within the family Araceae (though some authors prefer to put duckweeds into their own separate family, Lemnaceae; Sree et al., 2016). They are found in lentic and slow-moving freshwater systems around the world and are particularly successful in systems subject to cultural eutrophication. The duckweed traits that are most broadly useful in ecology and evolution are an extremely short lifespan and rapid rate of asexual growth. Duckweeds are ranked among the fastest growing and most productive higher plants (e.g., Ziegler et al., 2015), often completely blanketing the surface of their water body (Fig. 1). This rapid growth is part of what makes duckweed useful for industrial applications, but is also advantageous for fundamental research in ecology and evolution because it allows for a quick buildup of large sample sizes. Furthermore, the short lifespan of individual ramets makes it possible to track cohorts longitudinally and even multigenerationally, allowing in a matter of months the collection of data that would take years to obtain even in annual plants. For example, the relative ease of tracking cohorts over multiple generations has made duckweeds ideal for studying parental age effects in the contexts of both senescence (Ashby and Wangermann, 1949; Barks and Laird, 2015) and bet hedging (Mejbel and Simons, 2018). Despite the dominance of asexual reproduction, populations of duckweed maintain relatively high levels of genetic diversity. For instance, Vasseur et al. (1993) sampled 157 unique genotypes of L. minor among eight small ponds in Ontario, Canada, separated by a maximum distance of just 12 km. In many parts of the world, at least a few duckweed species are locally abundant, with multiple duckweed species often co-occurring in distinct communities (Landolt, 1986). This diversity at multiple biological levels and spatial scales makes duckweed a good candidate for research on competition, coexistence, and the maintenance of biodiversity (e.g., Vasseur et al., 1995), as well as distributional ecology and biogeography (e.g., Keddy, 1976). Another trait that makes duckweeds amenable to research in ecology and evolution is the ability to tolerate a wide range of conditions, as might be supposed based on their widespread occurrence, and use as bioremediation agents in contaminated sites. One particular growth environment that can be useful for research in ecology and evolution is axenic culture (i.e., free of microorganisms), which allows for precise control over environmental conditions. Obtaining axenic cultures from wild-collected duckweed is straightforward (Bowker et al., 1980), and we have ourselves exploited this property to ensure constant environmental conditions in common garden experiments (Barks et al., 2018). Axenic culture is also useful in the study of plant microbiomes, a topic currently of intense interest (e.g., Gilbert et al., 2018). Finally, under axenic conditions, duckweed cultures can be maintained at low temperature for up to a year without requiring human intervention, which allows for simple long-term maintenance of stock cultures. Of course, no model system is perfect for all questions, and some of duckweed's limitations must also be acknowledged. For instance, some duckweed species pairs are difficult to distinguish based on morphology alone; they can reliably be distinguished using laboratory manipulations or molecular identification techniques, but these approaches require time and money. In addition, because individual plants are small and typically free-floating, it can be challenging to mark and track individuals in a laboratory setting, let alone in the wild. That said, we think it will be possible to conduct individual-based studies in the wild using mark–recapture techniques or floating structures to limit plant movement—approaches we hope to pursue in the future. Furthermore, computer vision-based approaches are likely to become increasingly feasible for tracking and quantifying duckweed. Another potential limitation is that it may be difficult to generate de novo genetic diversity in duckweeds due to low rates of mutation and recombination (Xu et al., 2018 [preprint]); however, there have been successful efforts at flower induction and artificial cross pollination in some duckweeds (e.g., Fu et al., 2017). Finally, generalizing results based on duckweeds to other plant taxa must be done with caution, as some of the traits that make duckweeds easy to study (e.g., their size and anatomical simplicity; Table 1) also make them somewhat unusual. Relatedly, some of the functional traits on which plant ecologists commonly rely for comparative analyses are absent in duckweeds or at least difficult to compare with other plant taxa (e.g., height, rooting depth, phenology). These potential criticisms should be taken seriously when attempting to extrapolate results; however, we do not see them as a serious bar to using duckweeds in the first place. Notwithstanding the long history of research on duckweeds in ecology and evolution (e.g., Table 2), their use in these disciplines has only “skimmed the surface” of possible applications. Indeed, despite what we argue are clear advantages to studying duckweeds, the ecology and evolution research communities have never coalesced around them to the extent of other fields such as ecotoxicology and bioremediation, where they continue to play a major role (Ziegler et al., 2016). Why not? Perhaps practitioners of ecology and evolution tend to favor theory and study species in which the mode of reproduction is primarily sexual; because duckweeds are almost exclusively clonal, they may not be a natural fit within the culture of these research communities. We also speculate that there may be more general resistance to model systems, particularly in ecology, compared to, say, molecular genetics or developmental biology (Fox, 2012 made a similar argument). Biodiversity is justifiably of perennial interest in ecology. Moreover, it is almost axiomatic that variation per se is often of direct focus in both ecology and evolution. It may be that these features predispose scientists in these disciplines away from model species, especially those like duckweeds whose charisma is subtle. Regardless, we think there are many fundamental questions in ecology and evolution for which duckweeds would be an ideal study system, particularly those whose study requires large sample sizes, short generation times, and easy experimental manipulability. To close with three representative examples, we foresee duckweeds as being highly profitable in studies on (1) experimental plant evolution, (2) processes that straddle the line between evolutionary and ecological timescales (an avenue beginning to be explored by S. P. Hart, M. M. Turcotte, and J. M. Levine [unpublished manuscript]), and (3) experimental tests of the effects of complex competitive networks (e.g., intransitive “rock–paper–scissors” competition) on strain or species coexistence. We thank Lonnie Aarssen, Andrew Simons, Martin Turcotte, Suzanne Chmilar, Jake Hayden, and Austin Paiha for comments on earlier drafts. We thank Dave Armitage, an anonymous reviewer, and Editor-in-Chief Pamela Diggle for helpful reviews. We thank Martin Turcotte for providing the photograph in Fig. 1D (used with his permission) and S. P. Hart, M. M. Turcotte, and J. M. Levine for providing their unpublished manuscript. Funding was provided by the Natural Sciences and Engineering Research Council of Canada (grant no. RGPIN-2015-05486).

Journal of Evolutionary BiologyVolume 31, Issue 5 p. 779-779 CorrigendumFree Access Corrigendum: A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor) This article corrects the following: A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor) P. M. Barks, R. A. Laird, Volume 29Issue 4Journal of Evolutionary Biology pages: 748-756 First Published online: January 26, 2016 First published: 10 May 2018 https://doi.org/10.1111/jeb.13276Citations: 1AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat The authors originally identified the strain of duckweed studied in Barks and Laird (2016) as Lemna minor. Subsequent DNA barcoding demonstrated that it was in fact Lemna turionifera (see Supplementary Appendix S2 in Barks et al. 2018). The two species are difficult to distinguish based on morphology (Landolt 1986, p. 275). This change is consistent with recently altered reports issued by the Alberta Biodiversity Monitoring Institute (http://abmi.ca/) regarding the presence of Lemna species in Alberta, Canada. The GenBank sequences associated with the strain (‘Water Building A’) used in Barks and Laird (2016) are MG000422 (atpF-atpH marker) and MG000496 (psbK-psbI marker). This change in species identification from L. minor to L. turionifera also affects Barks (2015) thesis chapters 3 and 5 (the other chapters have correct species identifications except when referring to chapters 3 and 5). This change does not affect Barks and Laird (2015). That study used strain ‘CPCC 492’ from the Canadian Phycological Culture Centre. It was originally identified as L. minor, and subsequent DNA barcoding confirmed this identification (see Appendix S2 in Barks et al. 2018). The hypotheses tested and the conclusions drawn are unchanged and apply equally well to L. turionifera as they did to L. minor. The authors apologize for any inconvenience caused by this error. Correspondence: Patrick M. Barks, Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark. e-mail: patrick.barks@gmail.com References Barks, P.M. 2015. Parental Age Effects and the Evolution of Senescence in Lemna minor. PhD thesis. University of Lethbridge, Lethbridge, Alberta, Canada. Barks, P.M., Dempsey, Z.W., Burg, T.B. & Laird, R.A. 2018. Among-strain consistency in the pace and shape of senescence in duckweed. J. Ecol. https://doi.org/10.1111/1365-2745.12937 Barks, P.M. & Laird, R.A. 2015. Senescence in duckweed: age-related declines in survival, reproduction, and offspring quality. Funct. Ecol. 29: 540– 548. Barks, P.M. & Laird, R.A. 2016. A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor). J. Evol. Biol. 29: 748– 756. Landolt, E. 1986. The family of Lemnaceae — A monographic study, vol. 1. Biosystematic investigations in the family of duckweeds (Lemnaceae) (vol. 2). Veröffentlichungen des Geobotanischen Institutes der ETH, Stiftung Rübel, Zürich. Citing Literature Volume31, Issue5May 2018Pages 779-779 ReferencesRelatedInformation

Summary As they grow old, most organisms experience progressive physiological deterioration resulting in declining rates of survival and reproduction – a seemingly maladaptive phenomenon known as senescence. Although senescence is usually defined with respect only to survival and reproduction, a third component of fitness, offspring quality, may also decline with age. Few studies, however, have assessed age‐related changes in offspring quality using measures that truly reflect fitness. In a controlled environment, we tested for age‐related declines in three demographic components of fitness (survival, reproduction and offspring quality) in Lemna minor, a small aquatic plant in the subfamily Lemnoideae (the duckweeds) with a short life span and rapid rate of asexual reproduction. Our primary measure of offspring quality, the intrinsic rate of increase, more closely approximates fitness than measures used in previous studies such as size, life span and total reproductive output. We observed strong age‐related declines in all three components of fitness: old plants had lower rates of survival and reproduction, and produced lower‐quality offspring than younger plants. Theoretical and empirical research on the evolutionary biology of senescence should devote more attention to offspring quality. This often unrecognized component of fitness may change with age – as we have shown in L. minor – and may be shaped by, and feed back into, the same evolutionary forces that give rise to senescence.

For many animals, the ability to distinguish cues indicative of predation risk from cues unrelated to predation risk is not entirely innate, but rather is learned and improved with experience. Two pathways to such learning are possible. First, an animal could initially express antipredator behaviour toward a wide range of cues and subsequently learn which of those cues are non-threatening. Alternatively, it could initially express no antipredator behaviour toward a wide range of cues and subsequently learn which of them are threatening. While the learned recognition of threatening cues may occur either through personal interaction with a cue (asocial learning) or through observation of the behaviour of social companions toward a cue (social learning), the learned recognition of non-threatening cues seems to occur exclusively through habituation, a form of asocial learning. Here, we tested whether convict cichlid fish (Amatitlania siquia) can socially learn to recognize visual cues in their environment as either threatening or non-threatening. We exposed juvenile convict cichlids simultaneously to a novel visual cue and one of three (visual) social cues: a social cue indicative of non-risk (the sight of conspecifics that had previously been habituated to the novel cue), a social cue indicative of predation risk (the sight of conspecifics trained to fear the novel cue), or a control treatment with no social cue. The subsequent response of focal fish, when presented with the novel cue alone, was not influenced by the social cue that they had previously witnessed. We therefore did not find evidence that convict cichlids in our study could use social learning to recognize novel visual cues as either threatening or non-threatening. We consider alternative explanations for our findings.

Fisheries for yellow perch Perca flavescens are economically important in North America, but in many lakes this species does not attain sizes desirable to anglers (total length [TL] > 250 mm). We investigated factors potentially contributing to the lack of angling-sized yellow perch in Dore Lake, Saskatchewan. This large boreal lake has a long history of exploitation and is subject to current controversy regarding the impact of double-crested cormorants Phalacrocorax auritus on its fisheries. We found that yellow perch in Dore Lake attained greater maximum ages (mean +/- SD = 7.4 +/- 1.0 years) but smaller maximum sizes (215 +/- 7 mm TL) than other yellow perch populations. Thus, the lack of angling-sized yellow perch in Dore Lake is probably the result of slow growth rates rather than short life spans. Double-crested cormorants preyed heavily on yellow perch, but predation was highly skewed toward much smaller sizes (<100 mm TL) than those preferred by anglers. Stomach contents and stable nitrogen isotopes confirmed that yellow perch in Dore Lake undergo expected ontogenetic diet shifts and become predominantly piscivorous at around age 3. Analysis with stable isotopes also revealed long-term dietary differences between age-2 and age-3 yellow perch captured in littoral versus offshore habitats, suggesting some degree of intrapopulation variability in resource and habitat use among yellow perch in Dore Lake.